Area sensor and display apparatus provided with an area sensor

ABSTRACT

An area sensor of the present invention has a function of displaying an image in a sensor portion by using light-emitting elements and a reading function using photoelectric conversion devices. Therefore, an image read in the sensor portion can be displayed thereon without separately providing an electronic display on the area sensor. Furthermore, a photoelectric conversion layer of a photodiode according to the present invention is made of an amorphous silicon film and an N-type semiconductor layer and a P-type semiconductor layer are made of a polycrystalline silicon film. The amorphous silicon film is formed to be thicker than the polycrystalline silicon film. As a result, the photodiode according to the present invention can receive more light.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an area sensor (semiconductordevice) having an image sensor function and a display function. Inparticular, the present invention relates to an area sensor(semiconductor device) that has EL (electroluminescence) elements as alight source and is composed of photoelectric conversion devicesprovided on a flat surface (insulating surface) and a plurality of thinfilm transistors (TFTs) arranged in a matrix.

[0003] 2. Description of the Related Art

[0004] In recent years, a solid-state image sensing device is beingused, which has diodes, CCDs, or the like for reading an electric signalhaving image information from a light signal having textural/graphicinformation, video information, and the like on a sheet of paper. Such asolid-state image sensing device is used for a scanner, a digitalcamera, and the like.

[0005] The solid-state image sensing device having photoelectricconversion devices are classified into a line sensor and an area sensor.In the line sensor, photoelectric conversion devices provided in a lineshape are scanned with respect to a subject, whereby image informationis captured as an electric signal.

[0006] The area sensor is also called a contact-type area sensor, inwhich photoelectric conversion devices provided on a flat surface aredisposed on a subject, and image information is captured as an electricsignal. Unlike the line sensor, it is not required to scan photoelectricconversion devices in the area sensor, so that a motor and the like forscanning are not necessary.

[0007]FIGS. 23A and 23B show a configuration of a conventional areasensor. FIG. 23A is a perspective view of the area sensor, and FIG. 23Bis a cross-sectional view thereof. A sensor substrate 2501 withphotoelectric conversion devices formed thereon, a backlight 2502, and alight scattering plate 2503 are provided as shown in FIG. 23B.

[0008] Light from the backlight 2502 (light source) is refracted in thelight scattering plate 2503, and is radiated to a subject 2504. Theradiated light is reflected from the subject 2504, and radiated to thephotoelectric conversion devices provided on the sensor substrate 2501.When the photoelectric conversion devices are irradiated with light, acurrent with a magnitude in accordance with the brightness of light isgenerated in the photoelectric conversion devices, and image informationof the subject 2504 is captured in the area sensor as an electricsignal.

[0009] In the above-mentioned area sensor, when light is not radiateduniformly to the subject from the backlight 2502, a read image maypartially become light or dark, resulting in inconsistencies of theimage. This makes it necessary to design the light scattering plate 2503so that light is radiated uniformly to the subject 2504, and toprecisely adjust the position of the backlight 2502, the lightscattering plate 2503, the sensor substrate 2501, and the subject 2504.

[0010] It is also difficult to minimize the size of the backlight 2502and the light scattering plate 2503, which prevents the area sensor frombecoming small, thin, and light-weight.

SUMMARY OF THE INVENTION

[0011] Therefore, with the foregoing in mind, it is an object of thepresent invention to provide an area sensor that is small, thin, andlight-weight, and in which a read image has no inconsistencies inlightness.

[0012] An area sensor of the present invention uses a photodiode as aphotoelectric conversion device. The area sensor also uses anelectroluminescense (EL) element as a light source.

[0013] In the present specification, a photodiode (photoelectricconversion device) includes an N-type semiconductor layer, a P-typesemiconductor layer, and a photoelectric conversion device provided soas to come into contact with a part of the N-type semiconductor layerand the P-type semiconductor layer.

[0014] When a photodiode is irradiated with light, the voltage thereofis decreased due to carriers generated by the light. At this time, aslight intensity is higher, the amount of a decrease in voltage becomeslarger. Furthermore, by comparing a voltage in the case where aphotodiode is irradiated with light, with a voltage in the case wherethe photodiode is not irradiated with light, a signal is input to asensor signal line.

[0015] An EL element (light-emitting element) is a spontaneouslight-emitting element, and is mainly used for an EL display. An ELdisplay is also called an organic EL display (OELD) or an organiclight-emitting diode (OLED).

[0016] An EL element has a configuration in which an EL layer (organiccompound layer) is interposed between a pair of electrodes (positiveelectrode and negative electrode), and the EL layer usually has amulti-layer configuration. Typically, there is a multi-layerconfiguration “hole transport layer/light-emitting layer/electrontransport layer” proposed by Tang of Eastman Kodak. This configurationhas a very high light-emitting efficiency, and most of the EL displayapparatuses that are being studied and developed adopt thisconfiguration.

[0017] Alternatively, an EL layer may have a configuration in which ahole injection layer, a hole transport layer, a light-emitting layer,and an electron transport layer are stacked in this order on anelectrode or a configuration in which a hole injection layer, a holetransport layer, a light-emitting layer, an electron transport layer,and an electron injection layer are stacked in this order on anelectrode. A light-emitting layer may be doped with a fluorescentcolorant or the like.

[0018] In the present specification, all the layers provided between apair of electrodes are collectively referred to as an “EL layer (organiccompound layer)”. Therefore, the above-mentioned hole injection layer,hole transport layer, light-emitting layer, electron transport layer,electron injection layer, etc. are all included in the EL layer. Apredetermined voltage is applied to an EL layer with the above-mentionedconfiguration through a pair of electrodes, whereby carriers arerecombined in a light-emitting layer to emit light.

[0019] In the present specification, an EL element (light-emittingelement) has a configuration in which an organic compound layer isinterposed between a pair of electrodes (positive electrode and negativeelectrode). The organic compound layer can be made of a knownlight-emitting material. Furthermore, the organic compound layer canhave a single-layer configuration and a multi-layer configuration.According to the present invention the organic compound layer may haveeither configuration. As luminescence in the organic compound layer,there are light emission (fluorescence) occurring when a singlet excitedstate is changed to a ground state and light emission (phosphorescence)occurring when a triplet excited state is changed to a ground state.According to the present invention, either light emission may be used.

[0020] Photodiodes and EL elements are provided on the same sensorsubstrate in a matrix. The photodiodes and the EL elements arecontrolled for operation, respectively, using thin film transistors(TFTs) similarly provided on the substrate in a matrix.

[0021] Light emitted from the EL elements is reflected from a subjectand radiated to the photodiodes. A current is generated by the lightradiated to the photodiodes, and an electric signal (image signal)having image information of the subject is captured by an area sensor.

[0022] According to the present invention, due to the above-mentionedconfiguration, light is radiated uniformly to a subject, so that noinconsistencies in lightness are caused in a read image. Furthermore, itis not required to provide a backlight and a light scattering plateseparately from a sensor substrate. Therefore, unlike a conventionalexample, an area sensor can be made small, thin, and light-weightwithout precisely adjusting the position of a backlight, a lightscattering plate, a sensor substrate, and a subject. Furthermore, themechanical strength of an area sensor is increased.

[0023] The area sensor of the present invention is also capable ofdisplaying an image, using the EL elements. The EL elements in thepresent invention have a function as a light source for reading an imageand a function as a light source for displaying an image. Therefore,even when an electronic display is not provided separately on the areasensor, an image can be displayed.

[0024] Examples of a film made of silicon include a single crystalsilicon film, a polycrystalline silicon film (polysilicon film), anamorphous silicon film (amorphous silicon film), etc. In the photodiodeaccording to the present invention, a photoelectric conversion layer ismade of an amorphous silicon film (amorphous silicon film), an N-typesemiconductor layer is made of an N-type polycrystalline silicon film(polysilicon film), and a P-type semiconductor layer is made of apolycrystalline silicon film (polysilicon film). The amorphous siliconfilm is thicker than the polycrystalline silicon film, and the ratio inthickness therebetween is preferably (1 to 10):1. In the photodiode usedin the present invention, a photoelectric conversion layer can receivemore light when the thickness of the amorphous silicon film is largerthan that of the polycrystalline silicon film.

[0025] According to the present invention, a photoelectric conversionlayer is made of an amorphous silicon film due to its high lightabsorptivity.

[0026] In a photodiode, a dark current (i.e., current flowing at a lightintensity of 0) may flow even when light is not radiated to thephotodiode. However, due to a high resistance of an amorphous siliconfilm, a current does not flow even under the condition of dark light,whereby a dark current can be decreased. More specifically, when a darkcurrent is small, a range of lightness and darkness of light which aphotodiode can receive is enlarged in the case of dark light.

[0027] As shown in FIG. 16, a metal film 280 can also be formed so as tocover a first interlayer insulating film 250 provided on a photoelectricconversion layer 248.

[0028] Light is radiated to a subject 270 from an EL element, and lightreflected form the subject 270 is radiated to a photodiode 306. However,in this case, among light passing through the photodiode 306, thereexists light that is not radiated to the photoelectric conversion layer248. If the metal film 280 is present as shown in FIG. 16, such light isreflected from the metal film 280, whereby the photoelectric conversionlayer 248 can receive it. Because of this, the photoelectric conversionlayer 248 can receive more light.

[0029] Hereinafter, the constitution of the present invention will bedescribed.

[0030] According to the present invention, there is provided an areasensor, characterized in that:

[0031] the sensor comprises a sensor portion provided with a pluralityof pixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

[0032] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0033] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0034] According to the present invention, there is provided an areasensor, characterized in that:

[0035] the sensor comprises a sensor portion provided with a pluralityof pixels each including a photodiode, an EL element, and a plurality ofthin film transistors;

[0036] the pixel includes a photodiode, an EL element, a switching TFY,an EL driving TFT, a reset TFT, a buffer TFT, and a selective TFT;

[0037] the switching TFT and the EL driving TFT control light emissionof the EL element;

[0038] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0039] the photodiode, the reset TFT, the buffer TFT, and the selectiveTFT generate an image signal from the light radiated to the photodiode;

[0040] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0041] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0042] According to the present invention, there is provided an areasensor, characterized in that:

[0043] the area sensor comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0044] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0045] a gate electrode of the switching TFT is connected to the gatesignal line;

[0046] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0047] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0048] a source region of the reset TFT is connected to the sensor powersource line;

[0049] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0050] a drain region of the buffer TFT is connected to the sensor powersource line;

[0051] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0052] a gate electrode of the selective TFT is connected to the sensorgate signal line,

[0053] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode,

[0054] an image signal generated from the light radiated to thephotodiode is input to the sensor output line,

[0055] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film, and

[0056] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0057] According to the present invention, there is provided an areasensor, characterized in that:

[0058] the area sensor comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0059] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0060] a gate electrode of the switching TFT is connected to the gatesignal line;

[0061] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0062] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0063] a source region of the reset TFT is connected to the sensor powersource line;

[0064] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0065] a drain region of the buffer TFT is connected to the sensor powersource line;

[0066] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0067] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0068] a polarity of the switching TFT is the same as that of theselective TFT;

[0069] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0070] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0071] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0072] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0073] According to the present invention, there is provided an areasensor, characterized in that:

[0074] the area sensor comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0075] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0076] a gate electrode of the switching TFT is connected to the gatesignal line;

[0077] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0078] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0079] a source region of the reset TFT is connected to the sensor powersource line;

[0080] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0081] a drain region of the buffer TFT is connected to the sensor powersource line;

[0082] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0083] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0084] the reset TFT and the selective TFT are switched from an ON stateto an OFF state or from an OFF state to an ON state by a signal input tothe reset gate signal line and the sensor gate signal line;

[0085] when one of the reset TFT and the selective TFT is in an ONstate, the other is in an OFF state;

[0086] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0087] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0088] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0089] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0090] According to the present invention, there is provided an areasensor, characterized in that:

[0091] the area sensor comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0092] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0093] a gate electrode of the switching TFT is connected to the gatesignal line;

[0094] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0095] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0096] a source region of the reset TFT is connected to the sensor powersource line;

[0097] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0098] a drain region of the buffer TFT is connected to the sensor powersource line;

[0099] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0100] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0101] a polarity of the switching TFT is the same as that of theselective TFT;

[0102] the reset TFT and the selective TFT are switched from an ON stateto an OFF state or from an OFF state to an ON state by a signal input tothe reset gate signal line and the sensor gate signal line;

[0103] when one of the reset TFT and the selective TFT is in an ONstate, the other is in an OFF state;

[0104] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0105] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0106] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0107] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0108] According to the present invention, there is provided a displaydevice, characterized in that:

[0109] the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0110] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer and is made of an amorphous semiconductor film; and

[0111] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0112] According to the present invention, there is provided a displaydevice, characterized in that:

[0113] the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0114] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, and a selective TFT;

[0115] the switching TFT and the EL driving TFT controls light emissionof the EL element;

[0116] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0117] the photodiode, the reset TFT, the buffer TFT, and the selectiveTFT generate an image signal from the light radiated to the photodiode;

[0118] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer and is made of an amorphous semiconductor film; and

[0119] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0120] According to the present invention, there is provided a displaydevice, characterized in that:

[0121] the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0122] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0123] a gate electrode of the switching TFT is connected to the gatesignal line;

[0124] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0125] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0126] a source region of the reset TFT is connected to the sensor powersource line;

[0127] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0128] a drain region of the buffer TFT is connected to the sensor powersource line;

[0129] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0130] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0131] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0132] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0133] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0134] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0135] According to the present invention, there is provided a displaydevice, characterized in that:

[0136] the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0137] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0138] a gate electrode of the switching TFT is connected to the gatesignal line;

[0139] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0140] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0141] a source region of the reset TFT is connected to the sensor powersource line;

[0142] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0143] a drain region of the buffer TFT is connected to the sensor powersource line;

[0144] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0145] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0146] a polarity of the switching TFT is the same as that of theselective TFT;

[0147] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0148] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0149] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0150] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0151] According to the present invention, there is provided a display.device, characterized in that:

[0152] the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0153] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0154] a gate electrode of the switching TFT is connected to the gatesignal line;

[0155] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0156] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0157] a source region of the reset TFT is connected to the sensor powersource line;

[0158] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0159] a drain region of the buffer TFT is connected to the sensor powersource line;

[0160] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0161] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0162] the reset TFT and the selective TFT are switched from an ON stateto an OFF state or from an OFF state to an ON state by a signal input tothe reset gate signal line and the sensor gate signal line;

[0163] when one of the reset TFT and the selective TFT is in an ONstate, the other is in an OFF state;

[0164] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0165] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0166] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0167] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0168] According to the present invention, there is provided a displaydevice, characterized in that:

[0169] the display apparatus comprises a sensor portion provided with aplurality of pixels each including a photodiode, an EL element, and aplurality of thin film transistors;

[0170] the pixel includes a photodiode, an EL element, a switching TFT,an EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a sourcesignal line, a gate signal line, a power supply line kept at a constantpotential, a reset gate signal line, a sensor gate signal line, a sensoroutput line connected to a constant current power source, and a sensorpower source line kept at a constant potential;

[0171] a gate electrode of the switching TFT is connected to the gatesignal line;

[0172] one of a source region and a drain region of the switching TFT isconnected to the source signal line, and the other is connected to agate electrode of the EL driving TFT;

[0173] a source region of the EL driving TFT is connected to the powersupply line, and a drain region of the EL driving TFT is connected tothe EL element;

[0174] a source region of the reset TFT is connected to the sensor powersource line;

[0175] a drain region of the reset TFT is connected to a gate electrodeof the buffer TFT and the photodiode;

[0176] a drain region of the buffer TFT is connected to the sensor powersource line;

[0177] one of a source region and a drain region of the selective TFT isconnected to the sensor output line, and the other is connected to asource region of the buffer TFT;

[0178] a gate electrode of the selective TFT is connected to the sensorgate signal line;

[0179] a polarity of the switching TFT is the same as that of theselective TFT;

[0180] the reset TFT and the selective TFT are switched from an ON stateto an OFF state or from an OFF state to an ON state by a signal input tothe reset gate signal line and the sensor gate signal line;

[0181] when one of the reset TFT and the selective TFT is in an ONstate, the other is in an OFF state;

[0182] light emitted from the EL element is reflected from a subject tobe radiated to the photodiode;

[0183] an image signal generated from the light radiated to thephotodiode is input to the sensor output line;

[0184] the photodiode includes a photoelectric conversion layer that isin contact with a part of a P-type semiconductor layer and an N-typesemiconductor layer, and is made of an amorphous semiconductor film; and

[0185] the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.

[0186] These and other advantages of the present invention will becomeapparent to those skilled in the art upon reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0187] In the accompanying drawings:

[0188]FIG. 1 is a circuit diagram of a sensor portion;

[0189]FIG. 2 is a circuit diagram of a pixel;

[0190]FIG. 3 is a timing chart of reading of an image in the sensorportion;

[0191]FIG. 4 is a timing chart of reading of a color image in the sensorportion;

[0192]FIG. 5 is a top view of an area sensor for digital driving;

[0193]FIG. 6 is a timing chart of light emission of an EL element whenan image is read;

[0194]FIG. 7 is a timing chart of light emission of an EL element whenan image is displayed;

[0195]FIG. 8 is a top view of an area sensor for analog driving;

[0196]FIG. 9 is a timing chart of light emission of an EL element whenan image is read;

[0197]FIGS. 10A to 10C show the steps of producing the sensor portion;

[0198]FIGS. 1A to 11C show the steps of producing the sensor portion;

[0199]FIGS. 12A to 12C show the steps of producing the sensor portion;

[0200]FIGS. 13A to 13C show the steps of producing the sensor portion;

[0201]FIGS. 14A and 14B show the steps of producing the sensor portion;

[0202]FIG. 15 is an enlarged view of a photodiode according to thepresent invention;

[0203]FIG. 16 is an enlarged view of a photodiode according to thepresent invention;

[0204]FIGS. 17A and 17B are top views of the sensor portion of an areasensor of the present invention;

[0205]FIGS. 18A to 18C show a schematic view and cross-sectional viewsof the sensor portion of the area sensor of the present invention;

[0206]FIGS. 19A to 19C show the production steps according to thepresent invention;

[0207]FIGS. 20A and 20B show the production steps according to thepresent invention;

[0208]FIGS. 21A and 21B show an outer appearance of a portable handscanner that is an exemplary area sensor of the present invention;

[0209]FIG. 22 shows an outer appearance of an area sensor provided witha touch panel that is an exemplary area sensor of the present invention;

[0210]FIGS. 23A and 23B are a perspective view and a cross-sectionalview of a conventional area sensor;

[0211]FIG. 24 is a circuit diagram of a sensor portion; and

[0212]FIGS. 25A to 25C show exemplary electronic equipment to which thepresent invention is applicable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0213] Hereinafter, the structure of an area sensor (semiconductordevice) of the present invention will be described. The area sensor ofthe present invention includes a sensor portion for reading an image anda driving portion for controlling driving of the sensor portion. FIG. 1shows a circuit diagram of the sensor portion according to the presentinvention.

[0214] A sensor portion 101 is provided with source signal lines SI toSX, power supply lines V₁ to V_(x), gate signal lines G₁ to G_(y), resetgate signal lines RG₁ to RG_(y), sensor gate signal lines SG₁ to SG_(y),sensor output lines SS₁ to SS_(x), and a sensor power source line VB.

[0215] The sensor portion 101 has a plurality of pixels 102. Each pixel102 includes one of the source signal lines S₁ to S_(x), one of thepower supply lines V₁ to V_(x), one of the gate signal lines G₁ toG_(y), one of reset the gate signal lines RG₁ to RG_(y), one of thesensor gate signal lines SG₁ to SG_(y), one of the sensor output linesSS₁ to SS_(x), and the sensor power source line VB.

[0216] The sensor output lines SS₁ to SS_(x) are respectively connectedto constant current power sources 103 _(—1) to 103 _(—x).

[0217]FIG. 2 shows a detailed configuration of the pixel 102. A regionsurrounded by a dotted line is the pixel 102. A source signal line Sdenotes one of the source signal lines S₁ to S_(x). A power supply lineV denotes one of the power supply lines V₁ to V_(x). A gate signal lineG denotes one of the gate signal lines G₁ to G_(y). A reset gate signalline RG denotes one of the reset gate signal lines RG₁ to RG_(y). Asensor gate signal line SG denotes one of the sensor gate signal linesSG₁ to SG_(y). A sensor output line SS denotes one of sensor outputlines SS₁ to SS_(x).

[0218] The pixel 102 includes a switching TFT 104, an EL driving TFT105, and an EL element 106. In FIG. 2, although a capacitor 107 isprovided in the pixel 102, the capacitor 107 may not be provided.

[0219] The EL element 106 is composed of a positive electrode, anegative electrode, and an EL layer provided between the positiveelectrode and the negative electrode. In the case where the positiveelectrode is connected to a source region or a drain region of the ELdriving TFT 105, the positive electrode functions as a pixel electrodeand the negative electrode functions as a counter electrode. Incontrast, in the case where the negative electrode is connected to asource region or a drain region of the EL driving TFT 105, the positiveelectrode functions as a counter electrode and the negative electrodefunctions as a pixel electrode.

[0220] A gate electrode of the switching TFT 104 is connected to thegate signal line G. One of a source region and a drain region of theswitching TFT 104 is connected to the source signal line S, and theother is connected to the gate electrode of the EL driving TFT 105.

[0221] The source region of the EL driving TFT 105 is connected to thepower supply line V, and the drain region of the EL driving TFT 105 isconnected to the EL element 106. The capacitor 107 is provided so as tobe connected to the gate electrode of the EL driving TFT 105 and thepower supply line V.

[0222] The pixel 102 further includes a reset TFT 110, a buffer TFT 111,a selective TFT 112, and a photodiode 113.

[0223] A gate electrode of the reset TFT 110 is connected to the resetgate signal line RG. A source region of the reset TFT 110 is connectedto the sensor power source line VB. The sensor power source line VB isalways kept at a constant electric potential (reference potential). Adrain region of the reset TFT 110 is connected to the photodiode 113 anda gate electrode of the buffer TFT 111.

[0224] Although not shown in the figure, the photodiode 113 has anN-type semiconductor layer, a P-type semiconductor layer, and aphotoelectric conversion layer provided between the N-type semiconductorlayer and the P-type semiconductor layer. The drain region of the resetTFT 110 is connected to either the P-type semiconductor layer or theN-type semiconductor layer of the photodiode 113.

[0225] A drain region of the buffer TFT 111 is connected to the sensorpower source line VB, and is always kept at a constant referencepotential. A source region of the buffer TFT 111 is connected to asource region or a drain region of the selective TFT 112.

[0226] A gate electrode of the selective TFT 112 is connected to thesensor gate signal line SG. One of a source region and a drain region ofthe selective TFT 112 is connected to the source region of the bufferTFT 111 as described above, and the other is connected to the sensoroutput line SS. The sensor output line SS is connected to the constantcurrent power source 103 (one of the constant current power sources 103_(—1) to 10 _(—3)), and is always supplied with a constant current.

[0227] Hereinafter, a method for driving the area sensor of the presentinvention will be briefly described with reference to FIGS. 1 and 2.

[0228] The EL element 106 of the pixel 102 functions as a light sourceof the area sensor, and the switching TFT 104, the EL driving TFT 105,and the capacitor 107 control the operation of the EL element 106 as alight source.

[0229] Light emitted from the EL element 106 is reflected from asubject, and radiated to the photodiode 113 of the pixel 102. Thephotodiode 113 transforms the radiated light into an electric signalhaving image information. The electric signal having image informationgenerated in the photodiode 113 is captured in the area sensor as animage signal by the reset TFT 110, the buffer TFT 111, and the selectiveTFT 112.

[0230]FIG. 3 is a timing chart showing the operation of the reset TFT110, the buffer TFT 111, and the selective TFT 112. FIG. 3 shows atiming chart in which the reset ITFT 110 is an N-channel type TFT, thebuffer TFT 111 is a P-channel type TFT, and the selective TFT 112 is anN-channel type TFT. According to the present invention, the reset TFT110, the buffer TFT 111, and the selective TFT 112 may be an N-channeltype TFT or a P-channel type TFT. It is preferable that the polarity ofthe reset TFT 110 is opposite to that of the buffer TFT 111.

[0231] First, the reset TFTs 110 for pixels in the first line, connectedto the reset gate signal line RG₁, are turned on with a reset signalinput to the reset gate signal line RG₁. Then, the reference potentialof the sensor power source line VB is given to the gate electrodes ofthe buffer TFTs 111.

[0232] The selective TFTs 112 for the pixels in the first line,connected to the sensor gate signal line SG₁ are turned off with asensor signal input to the sensor gate signal line SG₁. Thus, the sourceregion of each buffer TFT 111 is kept at an electric potential obtainedby subtracting a potential difference VGS between the source region andthe gate region of the buffer TFT 111 from the reference potential. Inthe present specification, a period during which the reset TFTs 110 arein an ON state is referred to as a reset period.

[0233] Then, the electric potential of the reset signal input to thereset gate signal line RG₁ is changed, whereby all of the reset TFTs 110for the pixels in the first line are turned off. As a result, thereference potential of the sensor power source line VB is not given toeach gate electrode of the buffer TFTs 111 for the pixels in the firstline. In the present specification, a period during which the reset TFTs110 are in an OFF state is referred to as a sampling period ST. Inparticular, a period during which the reset TFTs 110 for the pixels inthe first line are in an OFF state is referred to as a sampling periodST₁.

[0234] During the sampling period ST₁, the electric potential of thesensor signal input to the sensor gate signal line SG₁ is changed, andthe selective TFTs 112 for the pixels in the first line are turned on.Thus, the source regions of the buffer TFTs 111 for the pixels in thefirst line are electrically connected to the sensor output line SS₁ viathe selective TFTs 112. The sensor output line SS₁ is connected to theconstant current power sources 103 _(—1). Therefore, each buffer TFT 111functions as a source follower, whereby the potential difference V_(GS)between the source region and the gate region of the buffer TFT 111becomes constant.

[0235] When light emitted from the EL elements 106 is reflected from asubject and radiated to the photodiodes 113 during the sampling periodST₁, a current flows through the photodiodes 113. Therefore, theelectric potential of the gate electrodes of the buffer TFTs 111 kept atthe reference potential during the reset period is increased inaccordance with the magnitude of a current generated in the photodiodes113.

[0236] A current flowing through each photodiode 113 is proportional tothe intensity of light radiated to the photodiode 113. Therefore, imageinformation of the subject is transformed to an electric signal as it isby the photodiode 113. The electric signal generated in the photodiode113 is input to the gate electrode of the buffer TFT 111.

[0237] The potential different V_(GS) between the source region and thegate region of the buffer TFT 111 is always kept constant. Therefore,the source region of the buffer TFT 111 is kept at an electric potentialobtained by subtracting the potential difference V_(GS) from theelectric potential of the gate electrode of the buffer TFT 111.Consequently, when the electric potential of the gate electrode of thebuffer TFT 111 is changed, the electric potential of the source regionof the buffer TFT 111 is also changed in accordance therewith.

[0238] The electric potential of the source region of the buffer TFT 111is input of the sensor output line SS₁ via the selective TFT 112 as animage signal.

[0239] Next, the reset TFTs 110 for the pixels in the first line,connected to the reset gate signal line RG₁, are turned on with a resetsignal input to the reset gate signal line RG₁, and a reset period isobtained again. Simultaneously, the reset TFTs 110 for pixels in thesecond line, connected to the reset gate signal line RG 2, are turnedoff with a reset signal input to the reset gate signal line RG₂, wherebya sampling period ST₂ starts.

[0240] During the sampling period ST₂, in the same way as in thesampling period ST₁, an electric signal having image information isgenerated in the photodiodes, and an image signal is input to the sensoroutput line SS₂.

[0241] When the above-mentioned operation is repeated, and the samplingperiod ST_(y) is completed, one image can be read as an image signal. Inthe present specification, a period during which all the samplingperiods ST₁ to ST_(y) are completed is referred to as a sensor frameperiod SF.

[0242] During each sampling period, it is required to allow the ELelement of each pixel to emit light. For example, it is important thatthe EL elements of the pixels in the first line emit light during atleast the sampling period ST₁. All the pixels may emit light during thesensor frame period SF.

[0243] In the case of an area sensor for reading a color image, a sensorportion has pixels corresponding to red (R), green (G), and blue (B)colors. Pixels corresponding to RGB colors have three kinds of ELelements corresponding to RGB colors. Alternatively, they have an ELelement for emitting white light and three kinds of RGB color filters.Alternatively they have an EL element for emitting blue light orblue-green light and a phosphor (fluorescent color transforming layer:CCM).

[0244] Light with RGB colors emitted from the pixels corresponding toRGB colors is radiated to a subject successively. Light of each of RGBcolors reflected from the subject is radiated to photodiodes of thepixels, and image signals corresponding to RGB colors are captured inthe area sensor.

[0245]FIG. 4 shows a timing chart showing the operation of the reset TFT110, the buffer TFT 111, and the selective TFT 112 of the area sensorfor reading a color image. FIG. 4 shows a timing chart in which thereset TFT 110 is an N-channel type TFT, the buffer TFT 111 is aP-channel type TFT, and the selective TFT 112 is an N-channel type TFT.

[0246] While EL elements of pixels corresponding to R emit light, allthe sampling periods ST₁ to ST_(y) appear. A period during which all thesampling periods ST₁ to ST_(y) are completed during a period in whichthe EL elements of the pixels corresponding to R emit light is referredto as an R sensor frame period SFr. During the R sensor frame periodSF_(r), an image signal corresponding to R is captured in the areasensor. During the R sensor frame SF_(r), pixels corresponding to G andB do not emit light.

[0247] Next, while EL elements of the pixels corresponding to G emitlight, all the sampling periods TS₁ to ST_(y) appear. A period duringwhich all the sampling periods ST₁ to ST_(y) are completed during aperiod in which the EL elements of the pixels corresponding to G emitlight is referred to as a G sensor frame period SF_(g). During the Gsensor frame period SF_(g), an image signal corresponding to G iscaptured in the area sensor. During the G sensor frame SF_(g), pixelscorresponding to R and B do not emit light.

[0248] Next, while EL elements of the pixels corresponding to B emitlight, all the sampling periods TS₁ to ST_(y) appear. A period duringwhich all the sampling periods ST₁ to ST_(y) are completed during aperiod in which the EL elements of the pixels corresponding to B emitlight is referred to as a B sensor frame period SF_(b). During the Bsensor frame period SF_(b), an image signal corresponding to B iscaptured in the area sensor. During the B sensor frame SF_(b), pixelscorresponding to R and G do not emit light.

[0249] A period during which all the R sensor frame period SF_(r), the Gsensor frame period SF_(g), and the B sensor frame period SF_(b) arecompleted is a sensor frame period SF. When the sensor frame period SFis completed, one color image can be read as an image signal.

[0250] Furthermore, during each sampling period, it is required to allowthe EL elements of the pixels corresponding to each color to always emitlight. For example, during the sampling period ST₁ in the B sensor frameperiod, it is important that the EL elements of the pixels correspondingto B among those in the first line always emit light. Pixelscorresponding to each color may always emit light during each of the R,G, and B sensor frame period (SF_(r), SF_(g), SF_(b)).

[0251] According to the present invention, due to the above-mentionedconstitution, light is radiated uniformly to a subject. Therefore,inconsistencies are not caused in lightness of a read image. It is notrequired to provide a backlight and a light scattering plate separatelyfrom a sensor substrate (i.e., substrate having an insulating surface onwhich EL elements and photoelectric conversion devices are provided).Therefore, unlike the conventional example, an area sensor itself can bemade small, thin, and light-weight without precisely adjusting theposition of the backlight, the light scattering plate, the sensorsubstrate, and the subject. The mechanical strength of the area sensoritself is also increased.

[0252] Furthermore, the area sensor of the present invention is capableof displaying an image in a sensor portion, using EL elements (lightsource). Therefore, an image read by photodiodes can be displayed in thesensor portion without separately providing an electronic display on anarea sensor, and a read image can be confirmed as soon as it is read.

[0253] Embodiments

[0254] Hereinafter, the present invention will be described by way ofillustrative embodiments with reference to the drawings.

[0255] Embodiment 1

[0256] A method of driving the switching TFT 104 and the EL driving TFT105, which control the operation of the EL element 106 shown in FIG. 2,is explained in Embodiment 1. Note that the structure of the sensorportion is the same as that of the embodiment mode, and therefore FIG. 1and FIG. 2 are referenced.

[0257]FIG. 5 shows a top view of an area sensor of Embodiment 1.Reference numeral 120 denotes a source signal line driving circuit,reference numeral 122 denotes a gate signal line driving circuit, andboth control the driving of the switching TFT 104 and the EL driving TFT105. Further, reference numeral 121 denotes a sensor source signal linedriving circuit, reference numeral 123 denotes a sensor gate signal linedriving circuit, and both control the driving of the reset TFT 110, thebuffer TFT 111, and the selection TFT 112. Note that the source signalline driving circuit 120, the gate signal line driving circuit 122, thesensor source signal line driving circuit 121, and the sensor gatesignal line driving circuit 123 are referred to as a driving portion.

[0258] The source signal line driving circuit 120 has a shift register120 a, a latch (A) 120 b, and a latch (B) 120 c. A clock signal (CLK)and a start pulse (SP) are inputted to the shift register 120 a in thesource signal line driving circuit 120. The shift register 120 agenerates timing signals in order based upon the clock signal (CLK) andthe start pulse (SP), and the timing signals are supplied one afteranother to downstream circuits.

[0259] Note that the timing signals from the shift register 120 a may bebuffer-amplified by a circuit such as a buffer (not shown in the figure)and then supplied one after another to the downstream circuits as thebuffer-amplified timing signals. The load capacitance (parasiticcapacitance) of a wiring to which the timing signals are supplied islarge because many of the circuits and elements are connected to thewiring. The buffer is formed in order to prevent dullness in the riseand fall of the timing signal, generated due to the large loadcapacitance.

[0260] The timing signals from the shift register 120 a are supplied tothe latch (A) 120 b. The latch (A) 120 b has a plurality of latch stagesfor processing a digital signal. The latch (A) 120 b writes in andmaintains digital signals in order simultaneously with the input of thetiming signals.

[0261] Note that the digital signals may be sequentially inputted to theplurality of latch stages of the latch (A) 120 b when the digitalsignals are taken in by the latch (A) 120 b. However, the presentinvention is not limited to this structure. A so-called division drivemay be performed, that is, the plurality of latch stages of the latch(A) 120 b is divided into a number of groups, and then the digitalsignals are parallel inputted to the respective groups at the same time.Note that the number of groups at this point is called a divisionnumber. For example, if the latch circuits are grouped into 4 stageseach, then it is called a 4-branch division drive.

[0262] The time necessary to complete writing of the digital signalsinto all the latch stages of the latch (A) 120 b is called a lineperiod. In other words, the line period is defined as a time intervalfrom the start of writing the digital data signals into the latchcircuit of the leftmost stage to the end of writing the digital signalsinto the latch of the rightmost stage in the latch (A) 120 b. In effect,the above-defined line period added with the horizontal retrace periodmay also be referred to as the line period.

[0263] After the completion of one line period, a latch signal issupplied to the latch (B) 120 c. In this moment, the digital signalswritten in and held by the latch (A) 120 b are sent all at once to thelatch (B) 120 c to be written in and held by all the latch stagesthereof.

[0264] Sequential writing-in of digital signals on the basis of thetiming signals from the shift register 120 a is again carried out to thelatch (A) 120 b after it has completed sending the digital signals tothe latch (B) 120 c.

[0265] During this second time one line period, the digital signalswritten in and held by the latch (B) 120 c are inputted to the sourcesignal lines S1 to Sx.

[0266] On the other hand, the gate signal line driving circuit 122 iscomposed of a shift register and a buffer (both not shown in thefigure). Depending on the situation, the gate signal line drivingcircuit 122 may have a level shifter in addition to the shift registerand the buffer.

[0267] In the gate signal line driving circuit 122, the gate signal issupplied to the buffer (not shown in the figure) from the shift register(also not shown in the figure), and this is supplied to a correspondinggate signal line. Gate electrodes of the switching TFTs 104 of one lineportion of pixels are connected to each of the gate signal lines G1 toGy. All of the switching TFTs 104 of the one line portion of pixels mustbe placed in an ON state simultaneously, and therefore a buffer in whicha large electric current can flow is used.

[0268] Note that the number of source signal line driving circuits andgate signal line driving circuits, their structure, and their operationare not limited to the structure shown by Embodiment 1. The area sensorof the present invention is capable of using a known source signal linedriving circuit and a known gate signal line driving circuit.

[0269] Next, a timing chart for a case of driving the switching TFT 104and the EL driving TFT 105 of the sensor portion by a digital method isshown in FIG. 6.

[0270] A period through which all of the pixels of the sensor portion101 emit light is referred to as one frame period F. The frame period isdivided into an address period Ta and a sustain period Ts. The addressperiod is a period in which a digital signal is inputted to all of thepixels during one frame period. The sustain period (also referred to asa turn-on period) denotes a period in which the EL elements emit lightor not in accordance with the digital signal inputted to the pixels inthe address period and display is performed.

[0271] The electric potential of the electric power source supply linesV1 to Vx is maintained at a predetermined electric potential (electricpower source potential).

[0272] First, in the address period Ta, the electric potential of theopposing electrode of the EL element 106 is maintained at the sameheight as the electric power source potential.

[0273] Then all of the switching TFTs 104 connected to the gate signalline G1 turn on in accordance with a gate signal inputted to the gatesignal line G1. A digital signal is next inputted from the source signalline driving circuit 120 to the source signal lines S1 to Sx. Thedigital signal inputted to the source signal lines S1 to Sx is inputtedto the gate electrodes of the EL driving TFTs 105 through the switchingTFTs 104 which are in an ON state.

[0274] Next, all of the switching TFTs 104 connected to the gate signalline G2 are placed in an ON state in accordance with a gate signalinputted to the gate signal line G2. The digital signal is then inputtedfrom the source signal line driving circuit 120 to the source signallines S1 to Sx. The digital signal inputted to the source signal linesS1 to Sx is inputted to the gate electrodes of the EL driving TFTs 105through the switching TFTs 104 which are in an ON state.

[0275] The above operations are repeated through the gate signal lineGy, the digital signal is inputted to the gate electrodes of the ELdriving TFTs 105 of all the pixels 102, and the address period iscompleted.

[0276] The sustain period begins simultaneously to the end of theaddress period Ta. All of the switching TFTs 104 are placed in an OFFstate in the sustain period.

[0277] Then, at the same time as the sustain period begins, the electricpotential of the opposing electrodes of all the EL elements has a heightof the electric potential difference between the electric power sourcepotential to the level at which the EL elements will emit light when theelectric potential of the electric power source is applied to the pixelelectrodes. Note that the electric potential difference between thepixel electrode and the opposing electrode is referred to as an ELdriving voltage in this specification. Further, the EL driving TFTs 105are placed in an ON state in accordance with the digital signal inputtedto the gate electrode of the EL driving TFTs 105 of each pixel.Therefore, the electric power source potential is applied to the pixelelectrodes of the EL elements, and the EL elements of all pixels emitlight.

[0278] One frame period is completed at the same time as the sustainperiod is completed. It is necessary that the pixels emit light in allof the sampling periods ST1 to STy with the present invention.Therefore, it is very important that the sensor frame period SF beincluded within the sustain period when using the digital driving methodof Embodiment 1.

[0279] Note that an explanation of a method of driving the area sensorfor reading in a single color image is explained in Embodiment 1, but acase of reading in a color image is similar. However, for the case of anarea sensor which reads in a color image, one frame period is dividedinto three subframe periods corresponding to RGB, and an address periodand a sustain period are formed in each subframe period. A digitalsignal is inputted to all of the pixels such that only the EL elementsof pixels corresponding to R will emit light, and only the EL elementsfor the color R perform light emission in the sustain period. Thesubframe periods for G and B are similar, and only EL elements of pixelscorresponding to the respective colors perform light emission in eachsustain period.

[0280] For the case of an area sensor which reads in a color image, itis important that each sustain period of the three subframe periodscorresponding to RGB contains a sensor frame period for R, G, and B(SFr, SFg, SFb), respectively.

[0281] Embodiment 2

[0282] A method of driving the switching TFT 104 and the EL driving TFT105 when displaying an image in the sensor portion 101 is explained inEmbodiment 2. Note that the structure of the sensor portion is the sameas the structure shown by the embodiment mode, and therefore FIG. 1 andFIG. 2 may be referenced.

[0283] A timing chart when performing display of an image in the sensorportion 101 in the area sensor of the present invention by a digitalmethod is shown in FIG. 7.

[0284] First, one frame period F is divided into N subframe periods SF1to SFN. The number of subframe periods in one frame period alsoincreases as the number of gray scales increases. Note that, when thesensor portion of the area sensor displays an image, one frame period Fdenotes a period during which all pixels of the sensor portion displayone image.

[0285] It is preferable that 60 or more frame periods be provided eachsecond for the case of Embodiment 2. By setting the number of imagesdisplayed each second to 60 or greater, it becomes possible to visuallysuppress image flicker.

[0286] The subframe period is divided into an address period Ta and asustain period Ts. The address period is a period within one subframeperiod during which a digital video signal is inputted to all pixels.Note that the digital video signal is a digital signal having imageinformation. The sustain period (also referred to as a turn-on period)denotes a period during which EL elements are placed in a state ofemitting light or not emitting light in accordance with the digitalvideo signal inputted to the pixels in the address period and display isperformed. Note that the digital video signal denotes the digital signalhaving image information.

[0287] The address periods Ta of SF1 to SFN are taken as address periodsTa1 to TaN, and the sustain periods Ts of SF1 to SFN are taken assustain periods Ts1 to TsN.

[0288] The electric potential of the electric power source supply linesV1 to Vx is maintained at a predetermined electric potential (electricpower source potential).

[0289] First, the electric potential of the opposing electrode of the ELelements 106 is maintained at the same height as the electric powersource potential in the address period Ta.

[0290] Next, all of the switching TFTs 104 connected to the gate signalline G1 are placed in an ON state in accordance with a gate signalinputted to the gate signal line G1. The digital video signal is theninputted to the source signal lines S1 to Sx from the source signal linedriving circuit 102. The digital video signal has “0” or “1”information, and one of the “0” and “1” digital video signals is asignal having a “HI” voltage, while the other is a signal having a “LO”voltage.

[0291] The digital video signal inputted to the source signal lines S1to Sx is then inputted to the gate electrodes of the EL driving TFTs 105through the switching TFTs 104 in an ON state.

[0292] All of the switching TFTs 104 connected to the gate signal lineG1 are then placed in an OFF state, and all of the switching TFTs 104connected to the gate signal line G2 are placed in an ON state inaccordance with a gate signal inputted to the gate signal line G2. Thedigital video signal is then inputted to the source signal lines S1 toSx from the source signal line driving circuit 102. The digital videosignal inputted to the source signal lines S1 to Sx is inputted to thegate electrodes of the EL driving TFTs 105 through the switching TFTs104 in an ON state.

[0293] The above operations are repeated through the gate signal lineGy, and the digital video signal is inputted to the gate electrodes ofthe EL driving TFTs 105 of all the pixels 102, and the address period iscompleted.

[0294] The sustain period Ts begins simultaneously with the completionof the address period Ta. All of the switching TFTs 104 are in an OFFstate in the sustain period. The electric potential of the opposingelectrodes of all the EL elements has a height of the electric potentialdifference between the electric power source potential to the level atwhich the EL elements will emit light when the electric potential of theelectric power source is applied to the pixel electrodes.

[0295] When the digital video signal has “0” information, the EL drivingTFT 105 is placed in an OFF state in Embodiment 2. The pixel electrodeof the EL elements is therefore maintained at the electric potential ofthe opposing electrode. As a result, the EL element 106 does not emitlight when the digital video signal having “0” information is inputtedto the pixel.

[0296] On the other hand, when the digital video signal has “1”information, the EL driving TFTs 105 are placed in an ON state. Theelectric power source potential is therefore applied to the pixelelectrode of the EL element 106. As a result, the EL element 106 of thepixel into which the digital video signal having “1” information isinputted emits light.

[0297] The EL elements are thus placed in a state in which they emitlight or do not emit light in accordance with the information of thedigital video signal input to the pixels, and the pixels performdisplay.

[0298] One subframe period is complete at the same time as the sustainperiod is complete. The next subframe period then appears, and onceagain the address period begins. The sustain period again beings afterthe digital video signal is input to all of the pixels. Note that theorder of appearance of the subframe periods SF1 to SFn is arbitrary.

[0299] Similar operations are then repeated in the remaining subframeperiods, and display is performed. After completing all of the nsubframe periods, one image is displayed, and one frame period iscompleted. When one frame period is complete, the subframe period of thenext frame period appears, and the above stated operations are repeated.

[0300] The lengths of the address periods Ta1 to Tan of the respective nsubframe periods are each the same in the present invention. Further,the ratio of lengths of the n sustain periods Ts1, . . . , Tsn isexpressed as Ts1:Ts2:Ts3 . . . :Ts(n-1):Tsn=2⁰:2⁻¹:2⁻²: . . .:2^(−(n-2):)2^(−(n-1)).

[0301] The gray-scale of each pixel is determined in accordance withduring which subframe periods in one frame period the pixel is made toemit light. For example, when n=8, and taking the brightness of pixelswhich emit light in all of the sustain periods as having a value of100%, pixels which emit light in Ts1 and Ts2 can express a brightness of75%, and for a case of selecting Ts3, Ts5, and Ts8, a brightness of 16%can be expressed.

[0302] Note that it is possible to freely combine Embodiment 2 withEmbodiment 1.

[0303] Embodiment 3

[0304] The electric potential of the opposing electrodes are maintainedat the same electric potential as that of the electric power sourcepotential during the address period in Embodiments 1 and 2. Therefore,the EL elements do not emit light. However, the present invention is notlimited to this structure. If an electric potential difference is alwaysformed between the opposing electric potential and the electric powersource potential, on an order at which the EL elements will emit light,when the electric power source potential is applied to the pixelelectrodes, display may also be performed in the address period, similarto the display period.

[0305] However, when combining Embodiment 1, in which the EL elementsare used as the light source of the area sensor, with Embodiment 3, itis important that the sensor frame period SF be contained within theframe period for an area sensor which reads in a single color image.Furthermore, it is important that the three subframe periodscorresponding to RGB be contained in R, G, and B sensor frame periods,respectively, for an area sensor which reads in a color image.

[0306] In addition, when combining Embodiment 2, in which an image isdisplayed in the sensor portion, with Embodiment 3, the entire subframeperiod in practice becomes a period for performing display, andtherefore the lengths of the subframe periods are set so as to beSF1:SF2:SF3: . . . :SF(n-1):SF =2⁰:2⁻¹:2⁻²: . . .:2^(−(n-2)):2^(−(n-1)). An image having a high brightness can beobtained in accordance with the above structure when compared with thedrive method in which light is not emitted during the address period.

[0307] Embodiment 4

[0308] An example of a method of driving the switching TFTs 104 and theEL driving TFTs 105, which control the operation of the EL elements 106shown in FIG. 2, by a method which differs from that of Embodiment 1 isexplained in Embodiment 4. Note that the structure of the sensor portionis the same as that shown by the embodiment mode, and therefore FIG. 1and FIG. 2 may be referenced.

[0309] A top view of an area sensor of Embodiment 4 is shown in FIG. 8.Reference numeral 130 denotes a source signal line driving circuit,reference numeral 132 denotes a gate signal line driving circuit, andboth control the driving of the switching TFT 104 and the EL driving TFT105. Further, reference numeral 131 denotes a sensor source signal linedriving circuit, and reference numeral 133 denotes a sensor gate signalline driving circuit, and both control the driving of the reset TFT 110,the buffer TFT 111, and the selection TFT 112. One each of the sourcesignal line driving circuit and the gate signal line driving circuit areformed in Embodiment 4, but the present invention is not limited to thisstructure. Two source signal line driving circuits may also be formed.Further, two gate signal line driving circuits may also be formed.

[0310] Note that the source signal line driving circuit 130, the gatesignal line driving circuit 132, the sensor source signal line drivingcircuit 131, and the sensor gate signal line driving circuit 133 arereferred to as a driving portion throughout this specification.

[0311] The source signal line driving circuit 130 has a shift register130 a, a level shifter 130 b, and a sampling circuit 130 c. Note thatthe level shifter may be used when necessary, and it need notnecessarily be used. Further, a structure is used in Embodiment 4 inwhich the level shifter is formed between the shift register 130 a andthe sampling circuit 130 c, but the present invention is not limited tothis structure. A structure in which the level shifter 130 b isincorporated within the shift register 130 a may also be used.

[0312] A clock signal CLK and a start pulse signal SP are input to theshift register 130 a in the source signal line driving circuit 130. Asampling signal is output from the shift register 130 a in order tosample an analog signal. The output sampling signal is input to thelevel shifter 130 b, and it electric potential amplitude is increased,and it is output.

[0313] The sampling signal output from the level shifter 130 b is inputto the sampling circuit 130 c. The analog signal input to the samplingcircuit 130 c is then sampled by the sampling signal, and input tosource signal lines S1 to Sx.

[0314] On the other hand, the gate signal line driving circuit 132 has ashift register and a buffer (neither shown in the figure). Further, thegate signal line driving circuit 132 may also have a level shifter inaddition to the shift register and the buffer, depending upon thecircumstances.

[0315] In the gate signal line driving circuit 132, a gate signal issupplied to the buffer (not shown in the figure) from the shift register(also not shown in the figure), and this is supplied to a correspondinggate signal line. Gate electrodes of the switching TFTs 104 of one lineportion of pixels are connected to the gate signal lines G1 to Gy, andall of the switching TFTs 104 of the one line portion of pixels must beplaced in an ON state simultaneously, and therefore a buffer in which alarge electric current is capable of flowing is used.

[0316] Note that the number of source signal line driving circuits andgate signal line driving circuits, their structure, and their operationare not limited to the structure shown by Embodiment 4. The area sensorof the present invention is capable of using a known source signal linedriving circuit and a known gate signal line driving circuit.

[0317] Next, a timing chart for a case of driving the switching TFT 104and the EL driving TFT 105 of the sensor portion by an analog method isshown in FIG. 9. A period through which all of the pixels of the sensorportion display light is referred to as one frame period F. One lineperiod L denotes a period from the selection of one gate signal lineuntil the selection of the next, separate, gate signal line. For thecase of the area sensor shown in FIG. 2, there are y gate signal lines,and therefore y line periods L1 to Ly are formed within one frameperiod.

[0318] The number of line periods within one frame period increasesalong with increasing resolution, and the driving circuits must bedriven at a high frequency.

[0319] First, the electric potential of the electric power source supplylines V1 to Vx is maintained at the constant electric power sourcepotential. The opposing electric potential, the electric potential ofthe opposing electrodes of the EL elements 106, is also maintained at aconstant electric potential. The electric power source potential has anelectric potential difference with the opposing electric potential onthe order that the EL elements 106 will emit light when the electricpower supply potential is applied to the pixel electrodes of the ELelements 106.

[0320] In the first line period L1, all of the switching TFTs 104connected to the gate signal line G1 are placed in an ON state inaccordance with a gate signal input to the gate signal line G1 from thegate signal line driving circuit 132. The analog signal is then input tothe source signal lines S1 to Sx in order from the source signal linedriving circuit 130. The analog signal input to the source signal linesS1 to Sx is input to the gate electrodes of the EL driving TFTs 105through the switching TFTs 104 which are in an ON state.

[0321] The size of the electric current flowing in a channel formingregion of the EL driving TFTs 105 is controlled by the height of theelectric potential (voltage) of the signal input to the gate electrodesof the EL driving TFTs 105. Therefore, the electric potential applied tothe pixel electrodes of the EL elements 106 is determined by the heightof the electric potential of the analog signal input to the gateelectrodes of the EL driving TFTs 105. The EL elements 105 arecontrolled by the electric potential of the analog signal, and performthe emission of light. Note that, in the case of Embodiment 4, theanalog signal input to all of the pixels is maintained at an electricpotential having the same height.

[0322] The first line period L1 is complete when input of the analogsignal to the source signal lines S1 to Sx is completed. Note that theperiod until the input of the analog signal to the source signal linesS1 to Sx is complete may also be combined with a horizontal returnperiod and taken as one line period. The second line period L2 beginsnext, and all of the switching TFTs 104 connected to the gate signalline G1 are placed in an OFF state. All of the switching TFTs 104connected to the gate signal line G2 are then placed in an ON state inaccordance with a gate signal input to the gate signal line G2. Then,similar to the first line period L1, the analog signal is input in orderto the source signal lines S1 to Sx.

[0323] The above operations are repeated up through the gate signal lineGy, and all of the line periods L1 to Ly are complete. When all of theline periods L1 to Ly are completed, one frame period is complete. TheEL elements of all of the pixels perform light emission by completingone frame period. Note that all of the line periods L1 to Ly and avertical return period may also be combined and taken as one frameperiod.

[0324] It is necessary for the pixels to emit light in all of thesampling periods ST1 to STy with the present invention, and for the caseof the driving method of Embodiment 4, it is important that the sensorframe period SF is included within the frame period.

[0325] Note that an explanation of a method of driving an area sensorfor reading in a single color image is explained in Embodiment 4, but acase of reading in a color image is similar. However, for an area sensorwhich reads in a color image, one frame period is divided into threesubframe periods corresponding to RGB. An analog signal is then input toall of the pixels such that only the EL elements of pixels correspondingto R will emit light in an R subframe period, and only the EL elementsfor the color R perform light emission. The subframe periods for G and Bare similar, and only EL elements of pixels corresponding to therespective color perform light emission.

[0326] For the case of an area sensor which reads in a color image, itis important that each sustain period of the three subframe periodscorresponding to RGB contain a sensor frame period for R, G, and B (SFr,SFg, SFb), respectively.

[0327] Note that if an analog video signal having image information issubstituted for the analog signal for a case of displaying an image inthe sensor portion 101 in the driving method of Embodiment 4, display ofthe image in the sensor portion 101 becomes possible.

[0328] Embodiment

[0329]5

[0330] A cross sectional diagram of an area sensor of the presentinvention is explained in Embodiment 5.

[0331]FIG. 14B shows a cross sectional diagram of an area sensor ofEmbodiment 5. Reference numeral 301 denotes a switching TFT, referencenumeral 302 denotes an EL driving TFT, 303 denotes a reset TFT, 304denotes a buffer TFT, and reference numeral 305 denotes a selection TFT.

[0332] Further, reference numeral 242 denotes a p-type semiconductorlayer, 248 denotes a photoelectric conversion layer, and referencenumeral 238 denotes a n-type semiconductor layer. A photodiode 306 isformed by the p-type semiconductor layer 242, the photoelectricconversion layer 248, and the n-type semiconductor layer 238. Referencenumeral 265 denotes a sensor wiring, and the sensor wiring is connectedthe n-type semiconductor layer 238 and an external electric powersource. Further, the p-type semiconductor layer 242 of the photodiode306 and the drain region of the reset TFT 303 is connected each otherelectrically.

[0333] Further, reference numeral 264 denotes a pixel electrode (anode),266 denotes an EL layer and 267 denotes an opposing electrode (cathode).An EL element 269 is formed by the pixel electrode (anode) 264, the ELlayer 266 and the opposing electrode (cathode) 267. Note that referencenumeral 268 denotes a bank, and that the EL layers 266 of adjacentpixels are separated.

[0334] Reference numeral 270 denotes a subject, and light emitted fromthe EL element 269 is reflected by the subject 270 and is irradiated tothe photodiode 306. The subject 270 is formed on the side of a sensorsubstrate 200 on which the TFTs are not formed in Embodiment 5.

[0335] The switching TFT 301, the buffer TFT 304, and the selection TFT305 are all n-channel TFTs in Embodiment 5. Further, the EL driving TFT302 and the reset TFT 303 are a p-channel TFT. Note that the presentinvention is not limited to this structure. Therefore, the switching TFT301, the EL driving TFT 302, the buffer TFT 304, the selection TFT 305,and the reset TFT 303 may be either n-channel TFTs or p-channel TFTs.

[0336] However, when a source region or a drain region of the EL drivingTFT 302 is electrically connected to the anode 264 of the EL element269, as in Embodiment 5, it is preferable that the EL driving TFT 302 bea p-channel TFT. Conversely, when the source region or the drain regionof the EL driving TFT 302 is electrically connected to the cathode ofthe EL element 269, it is preferable that the EL driving TFT 302 be an-channel TFT.

[0337] Note the photodiode and the other TFTs of Embodiment 5 can beformed at the same time, and therefore the number of process steps canbe suppressed.

[0338] Note that it is possible to freely combine Embodiment 5 withEmbodiments 1 to 4.

[0339] Embodiment 6

[0340] A cross sectional diagram of an area sensor of the presentinvention, differing from that of Embodiment 5, is explained inEmbodiment 6.

[0341]FIG. 15 shows a cross sectional diagram of an area sensor ofEmbodiment 6. Reference numeral 701 denotes a switching TFT, referencenumeral 702 denotes an EL driving TFT, 703 denotes a reset TFT, 704denotes a buffer TFT, and reference numeral 705 denotes a selection TFT.

[0342] Further, reference numeral 738 denotes a n-type semiconductorlayer, 748 denotes a photoelectric conversion layer, and referencenumeral 742 denotes a p-type semiconductor layer. A photodiode 706 isformed by the n-type semiconductor layer 738, the photoelectricconversion layer 748, and the p-type semiconductor layer 742. Referencenumeral 765 denotes a sensor wiring, and the sensor wiring electricallyconnects the p-type semiconductor layer 742 and an external electricpower source. Further, the n-type semiconductor layer 738 of thephotodiode 706 and a drain region of the reset TFT 703 are electricallyconnected.

[0343] Reference numeral 767 denotes a pixel electrode (cathode), 766denotes an EL layer, and 764 denotes an opposing electrode (anode). AnEL element 769 is formed by the pixel electrode (cathode) 767, the ELlayer 766, and the opposing electrode (anode) 764. Note that referencenumeral 768 denotes a bank, and that the EL layers 766 of adjacentpixels are separated.

[0344] Reference numeral 770 denotes a subject, and light emitted fromthe EL element 769 is reflected by the subject 770 and is irradiated tothe photodiode 706. Differing from Embodiment 5, the subject 770 isformed on the side of a substrate 700 on which the TFTs are formed inEmbodiment 6.

[0345] The switching TFT 701, the EL driving TFT 702, and the reset TFT703 are all n-channel TFTs in Embodiment 6. Further, the buffer TFT andthe selection TFT are p-channel TFTs. Note that the present invention isnot limited to this structure. Therefore, the switching TFT 701, the ELdriving TFT 702, the buffer TFT 704, the selection TFT 705, and thereset TFT 703 may be either n-channel TFT's or p-channel TFTs.

[0346] However, when a source region or a drain region of the EL drivingTFT 702 is electrically connected to the cathode 709 of the EL element769, as in Embodiment 6, it is preferable that the EL driving TFT 702 bea n-channel TFT. Conversely, when the source region or the drain regionof the EL driving TFT 702 is electrically connected to the anode 712 ofthe EL element 769, it is preferable that the EL driving TFT 702 be ap-channel TFT.

[0347] Furthermore, when the drain region of the reset TFT 703 iselectrically connected to the p-type semiconductor layer 742 of thephotodiode 706, as in Embodiment 6, it is preferable that the reset TFT703 be a n-channel TFT, and that the buffer TFT 704 be a p-channel TFT.Conversely, when the drain region of the reset TFT 703 is electricallyconnected to the p-type semiconductor layer 742 of the photodiode 702,and the sensor wiring 765 is connected to the n-type semiconductor layer738, it is preferable that the reset TFT 703 be a p-channel TFT, andthat the buffer TFT 704 be a n-channel TFT.

[0348] Note the photodiode 706 and the other TFTs of Embodiment 6 can beformed at the same time, and therefore the number of process steps canbe suppressed.

[0349] Note also that it is possible to freely combine Embodiment 6 withEmbodiments 1 to 5.

[0350] Embodiment 7

[0351] A method of producing a sensor portion of an area sensor of thepresent invention will be described with reference to FIGS. 10A to 14B.The sensor portion has switching TFTs 301, EL driving TFTs 302, resetTFTs 303, buffer TFTs 304, selective TFTs 305, and diodes 306 on thesame substrate.

[0352] First, referring to FIG. 10A, a substrate 200 made of glass suchas barium bolosilicate glass and aluminobolosilicate glass (e.g., #7059glass and #1737 glass produced by Coming) is used in this embodiment.The substrate 200 is not particularly limited as long as it has lighttransparency. A quartz substrate, a glass substrate, a ceramicsubstrate, or the like may be used. Furthermore, a plastic substrate maybe used, which has heat resistance that can withstand a treatmenttemperature in this embodiment.

[0353] As the substrate 200, a stainless substrate may be used. However,since a stainless substrate is not transparent, it is effective onlywhen an EL element 769 emits light upward as shown in FIG. 15.

[0354] An insulating film (underlying film) made of silicon oxide isformed on the substrate 200 so as to cover it. The insulating film canbe made of a silicon oxide film, a silicon nitride film, or a siliconoxide nitride film. For example, a silicon oxide nitride film made ofSiH₄, NH₃, and N₂O may be formed to a thickness of 250 to 800 nm(preferably, 300 to 500 nm) by plasma CVD. Similarly, a hydrogenatedsilicon oxide nitride film made of SiH₄ and N₂O may be formed to athickness of 250 to 800 nm (preferably, 300 to 500 nm). In thisembodiment, an insulating film made of silicon oxide is formed to athickness of 250 to 800 nm so as to have a single-layer configuration. Amaterial for the insulating film is not limited to silicon oxide.

[0355] Next, a flattening insulating film 201 is formed by polishing theinsulating film by a CMP method. The CMP method is conducted by a knownmethod. In polishing an oxide film, slurry of a solid-liquid dispersionsystem is generally used, in which an abrasive of 100 to 1000 nmφ isdispersed in an aqueous solution containing a reagent such as a pHregulator. In this embodiment, silica slurry (pH=10 to 11) is used, inwhich 20% by weight of fumed silica particles obtained by thermallydissolving silicon chloride gas in an aqueous solution with potassiumhydroxide added thereto are dispersed.

[0356] After the flattening insulating film 201 is formed, semiconductorlayers 202 to 208 are formed thereon. The semiconductor layers 202 to208 are obtained by forming a semiconductor film having an amorphousstructure by a known method (e.g., sputtering, LPCVD, plasma CVD, or thelike), crystallizing the semiconductor film by known crystallizationprocess (e.g., laser crystallization, thermal crystallization, thermalcrystallization using a catalyst such as nickel, or the like) to obtaina crystalline semiconductor film, and patterning the crystallinesemiconductor film to a desired shape. The semiconductor layers 202 to208 are formed to a thickness of 25 to 80 nm (preferably, 30 to 60 nm).Although there is no particular limit to a material for the crystallinesemiconductor film, a silicon or silicon germanium (Si_(x)Ge_(1-x))alloy may be preferably used. In this embodiment, an amorphous siliconfilm of 55 nm is formed by plasma CVD, and thereafter, a solutioncontaining nickel is held onto the amorphous silicon film. After theamorphous silicon film is dehydrogenated at 500° C. for one hour, thefilm is thermally crystallized at 550° C. for four hours. Furthermore,the amorphous silicon film is subjected to laser annealing for thepurpose of enhancing crystallization, whereby a crystalline silicon filmis formed. The crystalline silicon film is patterned by photolithographyto form the semiconductor layers 202 to 208.

[0357] After the semiconductor layers 202 to 208 are formed, they may bedoped with a trace amount of an impurity element (boron or phosphorus)so as to control the threshold values of TFTs.

[0358] In the case of producing a crystalline semiconductor film bylaser crystallization, a pulse-oscillation type or continuouslight-emitting type excimer laser, a YAG laser, and a YVO₄ layer can beused. In the case of using these lasers, a laser beam emitted from alaser oscillator may be condensed in a line shape by an optical systemand radiated to a semiconductor film. Conditions of crystallization areappropriately selected by those skilled in the art. However, in the caseof using an excimer laser, a pulse oscillation frequency is set to beseveral 300 Hz, and a laser energy density is set to be 100 to 400mJ/cm² (typically, 200 to 300 mJ/cm²). Furthermore, in the case of usinga YAG laser, the second harmonic thereof may be used, with a pulseoscillation frequency set at several 30 to 300 kHz, and a laser energydensity set at 300 to 600 mJ/cm² (typically 350 to 500 mJ/cm²). Then,laser beams condensed in a line shape with a width of 100 to 1000 μm(e.g., 400 μm) may be radiated to the entire surface of a substrate withan overlapped ratio of the line-shaped laser beams set at 50% to 98%.

[0359] Then, a gate insulating film 209 covering the semiconductorlayers 202 to 208 is formed. The gate insulating film 209 is formed ofan insulating film containing silicon with a thickness of 40 to 150 nmby plasma CVD or sputtering. In this embodiment, a silicon oxide nitridefilm (composition ratio: Si=32%, O=59%, N=7%, H=2%) is formed to athickness of 110 nm by plasma CVD. Needless to say, the gate insulatingfilm is not limited to a silicon oxide nitride film. Another insulatingfilm containing silicon may be used as a single-layer or multi-layerconfiguration.

[0360] In the case of using a silicon oxide film as the insulating film,the insulating film can be formed by mixing tetraethyl orthosilicate(TEOS) and O₂ by plasma CVD, setting a reaction pressure at 40 Pa and asubstrate temperature at 300° C. to 400° C., and allowing discharge tooccur at a high-frequency (13.56 MHz) power density of 0.5 to 0.8 W/cm².The silicon oxide film thus produced is subjected to thermal annealingat 400° C. to 500° C., thereby exhibiting satisfactory characteristicsas the gate insulating film.

[0361] Then, as shown in FIG. 10A, a first conductive film 210 a(thickness: 20 to 100 nm) and a second conductive film 210 b (thickness:100 to 400 nm) are, stacked on the gate insulating film 209. In thisembodiment, the first conductive film 210 a made of a TaN film with athickness of 30 nm and the second conductive film 210 b made of a W filmwith a thickness of 370 nm are stacked. The TaN film is formed bysputtering using Ta as a target in a nitrogen atmosphere. The W film isformed by sputtering using W as a target. The W film can also be formedby thermal CVD, using tungsten hexafluoride (WF₆). In any case, the Wfilm needs to have a low resistance so as to be used as a gateelectrode, and the resistance of the W film is desirably 20 μΩcm orless. By enlarging crystal particles, the W film is allowed to have alow resistance. However, in the case where a number of impurity elementssuch as oxygen are present in the W film, crystallization of the W filmis inhibited to have a high resistance. Thus, in this embodiment, the Wfilm is formed by sputtering using W with a high purity (99.9999%) as atarget in such a manner that impurities are not mixed from a vapor phaseduring film formation, whereby the resistance of 9 to 20 μΩcm of the Wfilm can be realized.

[0362] In this embodiment, although the first conductive film 210 a ismade of TaN, and the second conductive film 210 b is made of W, there isno particular limit to the materials. The first and second conductivefilms 210 a and 210 b may be made of an element selected from Ta, W, Ti,Mo, Al, Cu, Cr, and Nd, or an alloy material or a compound materialcontaining the element as a main component. Furthermore, a semiconductorfilm such as a polycrystalline silicon film doped with an impurityelement such as phosphorus may be used. An AgPdCu alloy may also beused. Furthermore, it may be possible that the first conductive film ismade of a tantalum (Ta) film, and the second conductive film is made ofa W film. It may also be possible that the first conductive film is madeof a titanium nitride (TiN) film, and the second conductive film is madeof a W film. It may also be possible that the first conductive film ismade of tantalum nitride (TaN) film, and the second conductive film ismade of an Al film. It may also be possible that the first conductivefilm is made of a tantalum nitride (TaN) film, and the second conductivefilm is made of a Cu film.

[0363] Next, a mask 211 made of a resist is formed by photolithography,and first etching process for forming electrodes and wiring is conducted(FIG. 10B). The first etching process is conducted under first andsecond etching conditions. In this embodiment, under the first etchingcondition, an inductively coupled plasma (ICP) etching method is used,CF₄, Cl₂, and O₂ are used as etching gas, a gas flow ratio thereof isset at 25/25/10 (sccm), and a coil-shaped electrode is supplied with anRF (13.56 MHz) power of 500 W under a pressure of 1 Pa to generateplasma, whereby etching is conducted. The substrate side (sample stage)is also supplied with an RF (13.56 MHz) power of 150 W, whereby asubstantially negative self-bias voltage is applied. The W film isetched under the first etching condition, thereby forming taperedportions in a first conductive layer. An etching speed with respect to Wunder the first etching condition is 200.39 nm/min, and an etching speedwith respect to TaN is 80.32 nm/min, and a selection ratio of W withrespect to TaN is about 2.5. Furthermore, the taper angle of W becomesabout 26° under the first etching condition.

[0364] In the first etching process, by forming the mask 211 made of aresist in an appropriate shape, the ends of the first conductive layerand the second conductive layer are tapered due to the effect of thebias voltage applied to the substrate side. The angle of the taperedportion may be 15° to 45°. Thus, first-shaped conductive layers 212 to216 composed of first conductive layers 212 a to 216 a and secondconductive layers 212 b to 216 b are formed by the first etchingprocess. Reference numeral 217 denotes a gate insulating film, andregions not covered with the first-shaped conductive layers 212 to 216are etched by about 20 to 50 nm, whereby thin regions are formed.

[0365] Then, second etching process is conducted without removing themask made of a resist (FIG. 10C). Herein, CF₄, Cl₂, and O₂ are used asetching gas, a gas flow ratio thereof is set at 25/25/10 (sccm), and acoil-shaped electrode is supplied with an RF (13.56 MHz) power of 500 Wunder a pressure of 1 Pa to generate plasma, whereby etching isconducted. The substrate side (sample stage) is also supplied with an RF(13.56 MHz) power of 20 W, whereby a substantially negative self-biasvoltage is applied. An etching speed with respect to W in the secondetching process is 124.62 nm/min, and an etching speed with respect toTaN is 20.67 nm/rnin, and a selection ratio of W with respect to TaN isabout 6.05. Thus, the W film is selectively etched. The taper angle of Wobtained by second etching becomes about 70°. During the second etchingprocess, second conductive layers 218 b to 222 b are formed. On theother hand, the first conductive layers 212 a to 216 a are hardly etchedto form first conductive layers 218 a to 222 a. Reference numeral 223denotes a gate insulating film, and regions not covered withsecond-shaped conductive layers 218 to 222 are etched by about 20 to 50nm, whereby thin regions are formed.

[0366] An electrode formed of the first conductive layer 218 a and thesecond conductive layer 218 b will become an N-channel type buffer TFT304 in the late step, and an electrode formed of the first conductivelayer 219 a and the second conductive layer 219 b will become anN-channel type selective TFT 305 in the later step. Similarly, anelectrode formed of the first conductive layer 220 a and the secondconductive layer 220 b will become a P-channel type reset TFT 303 in thelater step, an electrode formed of the first conductive layer 221 a andthe second conductive layer 221 b will become an N-channel typeswitching TFT 301 in the later step, and an electrode formed of thefirst conductive layer 222 a and the second conductive layer 222 b willbecome a P-channel type EL driving TFT 302 in the later step.

[0367] Then, first doping process is conducted to obtain a state in FIG.11A. Doping is conducted using the second conductive layers 218 b to 222b as a mask with respect to an impurity element, in such a manner thatthe impurity element is added to the semiconductor layers below thetaper portions of the first conductive layers 218 a to 222 a. There isno conductive layer above the semiconductor layers 205 and 206, so thatthese semiconductor layers are doped from above the gate insulating film223. In this embodiment, plasma doping is conducted using phosphorus asan impurity element at a dose amount of 3.5×10¹² and an acceleratingvoltage of 90 keV. Thus, low-concentration impurity regions 224 a to 228a, 229, and 230 not overlapped with the first conductive layers, andlow-concentration impurity regions 224 b to 228 b overlapped with thefirst conductive layers are formed in a self-alignmient manner. Theconcentration of phosphorus added to the low-concentration impurityregions 224 b to 228 b is 1×10¹⁷ to 1×10¹⁸ atoms/cm³, and has a gentleconcentration gradient along the thickness of the taper portions of thefirst conductive layers 218 a to 222 a. In the semiconductor layersoverlapped with the taper portions of the first conductive layers 218 ato 222 a, although the impurity concentration is slightly decreased fromthe ends of the taper portions of the first conductive layers 218 a to222 a, the concentration is substantially the same.

[0368] A mask 231 made of a resist is formed, and second doping processis conducted, whereby an impurity element providing an N-type to thesemiconductor layers is added (FIG. 11B). Doping may be conducted by iondoping or ion implantation. Ion doping is conducted under the conditionsof a dose amount of 1×10¹³ to 5×10¹⁵ atoms/cm², and an accelerationvoltage of 60 to 100 keV. In this embodiment, doping is conducted at adose amount of 1.5×10¹⁵ atoms/cm² and an acceleration voltage of 80 keV.As an impurity element providing an N-type, an element belonging to theGroup-XV, typically, phosphorus (P) or arsenic (As) is used. Herein,phosphorus (P) is used. In this case, the conductive layers 218 to 222function as a mask with respect to the impurity element providing anN-type, whereby high-concentration impurity regions 232 a to 236 a, 237,and 238, low-concentration impurity regions 232 b to 236 b notoverlapped with the first conductive layers, and low-concentrationimpurity regions 232 c to 236 c overlapped with the first conductivelayers are formed in a self-alignment manner. The high-concentrationimpurity regions 232 a to 236 a, 237, and 238 are supplied with animpurity element providing an N-type in a concentration range of 1×10²⁰to 1×10²¹ atoms/cm³.

[0369] It is not required that the semiconductor films to be a P-channeltype are doped with an N-type impurity in the second doping processshown in FIG. 11B. Therefore, the mask 231 may be formed so as tocompletely cover the semiconductor layers 204, 206, and 208, therebypreventing the semiconductor layers 204, 206, and 208 from being dopedwith an N-type impurity. Alternatively, the mask 231 is not providedabove the semiconductor layers 204, 206 and 208, and the polaritythereof may be reversed in third doping process.

[0370] Then, the mask 231 made of a resist is removed, and a mask 239made of a resist is newly formed to conduct third doping process.Because of the third doping process, impurity regions 240 a to 240 c,241 a to 241 c, and 242 are formed, in which an impurity elementproviding a conductivity (P-type) opposite to the above-mentionedconductivity (N-type) is added to the semiconductor layers to be activelayers of P-channel type TFTs (FIG. 11C). The first conductive layers220 b and 222 b are used as a mask with respect to an impurity element,and an impurity element providing a P-type is added to form impurityregions in a self-alignment manner. There of no conductive layer abovethe impurity region 242, so that the impurity region 242 is doped fromabove the gate insulating film 223. In this embodiment, the impurityregions 240 a to 240 c, 241 a to 241 c, and 242 are formed by ion dopingusing diborane (B₂H₆). During the third doping process, thesemiconductor layers to form N-channel type TFTs are covered with themask 239 made of a resist. During the first and second doping process,the impurity regions 240 a, 240 b, and 240 c are supplied withphosphorus in different concentrations. However, by conducting doping sothat the concentration of the impurity element providing a P-typebecomes 2×10²⁰ to 2×10²¹ atoms/cm³ in any region, there is no problemfor these regions to function as source regions and drain regions ofP-channel type TFTs.

[0371] Then, the impurity element added to the respective semiconductorlayers is activated. Activation is conducted by thermal annealing usingan annealing furnace. Thermal annealing may be conducted in a nitrogenatmosphere with an oxygen concentration of 1 ppm or less (preferably,0.1 ppm or less) at 400° C. to 700° C. (typically, 500° C. to 550° C.).In this embodiment, activation is conducted by heat treatment at 550° C.for four hours. In addition to thermal annealing, laser annealing orrapid thermal annealing (RTA method) can be applied.

[0372] Furthermore, activation may be conducted after forming a firstinterlayer insulating film. In the case where a wiring material used forwiring is weak to heat, it is preferable to conduct activation afterforming an interlayer insulating film (insulating film mainly containingsilicon, e.g., silicon nitride film) in order to protect wiring and thelike, as in this embodiment.

[0373] Furthermore, heat treatment is conducted at 300° C. to 550° C.for 1 to 12 hours in an atmosphere containing 3% to 100% hydrogen,whereby the semiconductor layers are hydrogenated. In this embodiment,heat treatment is conducted at 410° C. for one hour in a nitrogenatmosphere containing about 3% hydrogen. In this step, unpairedconnecting ends of the semiconductor layers are terminated withthermally excited hydrogen. As another hydrogenation means, there isplasma hydrogenation (using hydrogen excited with plasma).

[0374] Furthermore, hydrogenation may be conducted after a passivationfilm is formed.

[0375] During the above-mentioned steps, impurity regions are formed inthe respective semiconductor layers.

[0376] Then, the mask 239 made of a resist is removed to conduct thirdetching process. In this embodiment, using the conductive layers 218 to222 as a mask, the gate insulating film is etched.

[0377] Because of the third etching process, gate insulating films 243 cto 247 c are formed under the second conductive layers 243 b to 247 b(FIG. 12A).

[0378] Then, a passivation film 271 is formed so as to cover thesubstrate 200 (FIG. 12B). The passivation film 271 can be made of asilicon oxide film, a silicon nitride film, or a silicon oxide nitridefilm. For example, a silicon oxide nitride film made of SiH₄, NH₃, andN₂O may be formed to a thickness of 10 to 800 nm (preferably, 50 to 500nm) by plasma CVD. Similarly, a hydrogenated silicon oxide nitride filmmade of SiH₄ and N₂O may be formed to a thickness of 50 to 800 nm(preferably, 10 to 500 nm). In this embodiment, the passivation filmmade of nitrogen oxide is formed to a thickness of 10 to 800 nm with asingle-layer configuration.

[0379] Then, a mask 272 made of a resist is formed by photolithography,and fourth etching process for forming an amorphous silicon film 248 isconducted. The resist mask 272 is formed so as to cover the substrate,and to come into contact with a part of the P-type semiconductor layer242 and the N-type semiconductor layer 238 (FIG. 12C). Then, only thesilicon nitride film is etched. In this embodiment, ICP etching is used,CF₄, Cl₂, and O₂ are used as etching gas, a gas flow ratio is set at40/60/35 (sccm), and a coil-shaped electrode is supplied with an RF(13.56 MHz) power of 500 W under the pressure of 1 Pa to generateplasma, whereby etching is conducted.

[0380] Then, the mask 272 made of a resist is removed. An amorphoussilicon film 248 is formed between the N-type semiconductor layer 242and the P-type semiconductor layer 238 so as to come into contact with apart of the N-type semiconductor layer 242 and the P-type semiconductorlayer 238 (FIG. 13A). The semiconductor film having an amorphousstructure is formed by a known method (e.g., sputtering, LPCVD, plasmaCVD, or the like). The amorphous silicon film 248 is formed to athickness, preferably one to ten times that of the N-channel typesemiconductor layer 242 and the P-channel type semiconductor layer 238.In this embodiment, the amorphous silicon film 248 is formed to athickness of 25 to 800 nm. Although there is no particular limit to amaterial for the crystalline semiconductor film, it may be preferablyformed of silicon or a silicon germanium (Si_(x)Ge_(1-x)) alloy. In thisembodiment, after an amorphous silicon film with a thickness of 55 nm isformed by plasma CVD, a solution containing nickel is held onto theamorphous silicon film.

[0381] Then, a first interlayer insulating film 235 is formed (FIG.13B). The first interlayer insulating film 235 is obtained by forming aninsulating film containing silicon to a thickness of 100 to 200 nm byplasma CVD or sputtering. In this embodiment, a silicon oxide nitridefilm with a thickness of 150 nm is formed by plasma CVD. Needless tosay, the first interlayer insulating film 235 is not limited to asilicon oxide nitride film. Another insulating film containing siliconmay be formed as a single-layer or multi-layer configuration.

[0382] Then, the first interlayer insulating film 249 is patterned so asto form contact holes reaching the impurity regions 232 a, 233 a, 235 a,238, 240 a, 241 a, and 242.

[0383] Then, source lines 251 to 256, and drain lines 257 to 262 areformed. In this embodiment, as these lines, a film mainly containing Alor Ag, or a material having excellent reflectivity such as a layeredfilm thereof are desirably used.

[0384] Then, as shown in FIG. 14A, a second interlayer insulating film249 is formed. By using resin such as polyimide, polyamide,polyimideamide, and acrylic resin, the second interlayer insulating film249 can have a flat surface. In this embodiment, a polyimide film with athickness of 0.7 μm is formed over the entire surface of the substrateas the second interlayer insulating film 249.

[0385] Next, as shown in FIG. 14B, a bank 268 made of a resin materialis formed. The bank 268 may be formed by patterning an acrylic film or apolyimide film with a thickness of 1 to 2 μm. The bank 268 may be formedalong the source line 256 or the gate line (not shown). The bank 268 maybe used as a shielding film by mixing a pigment or the like in the resinmaterial forming the bank 268.

[0386] Then, an EL layer 266 is formed. More specifically, an organic ELmaterial to be the EL layer 266 dissolved in a solvent such aschloroform, dichloromethane, xylene, toluene, tetrahydrofuran, and thelike is applied, and thereafter, the solvent is vaporized by heattreatment. Thus, a coating (EL layer) made of an organic EL material isformed.

[0387] In this embodiment, only one pixel is shown. However, alight-emitting layer emitting red light, a light-emitting layer emittinggreen light, and a light-emitting layer emitting blue light are formedsimultaneously with the formation of the EL layer. In this embodiment,as the light-emitting layer emitting red light,cyanopolyphenylenevinylene is formed to a thickness of 50 nm. Similarly,as the light-emitting layer emitting green light, polyphenylenevinyleneis formed to a thickness of 50 nm, and as the light-emitting layeremitting blue light, polyalkylphenylene is formed to a thickness of 50nm. Furthermore, 1,2-dichloromethane is used as a solvent, and thesolvent is vaporized by heat treatment with a hot plate at 80° C. to150° C. for 1 to 5 minutes.

[0388] In this embodiment, although the EL layer has a single-layerconfiguration, a hole injection layer, a hole transport layer, anelectron injection layer, an electron transport layer, and the like maybe additionally provided. Various examples of combinations have alreadybeen reported, and any configuration may be used.

[0389] After the EL layer 266 is formed, a positive electrode 267 madeof a transparent conductive film is formed to a thickness of 120 nm as acounter electrode. In this embodiment, a transparent conductive film isused, in which 10 to 20% by weight of zinc oxide is added to indiumoxide. The positive electrode 267 is preferably formed by vapordeposition at room temperature so as not to degrade the EL layer 266.

[0390] As described above, the buffer TFT 304, the selective TFT 305,the reset TFT 303, the diode 306, the switching TFT 301, the EL drivingTFT 302, and the EL element 269 can be formed on the same substrate.

[0391] In this embodiment, Embodiments 1 to 5 can be arbitrarilycombined.

[0392] Embodiment 8

[0393] In a method of producing a sensor portion of the area sensor ofthe present invention, a method of producing a photodiode different fromthat in Embodiment 6 will be described with reference to FIG. 16.

[0394]FIG. 16 is an enlarged view of a photodiode 306. As shown in FIG.16, in the photodiode 306, a metal film 280 is formed on a firstinterlayer insulating film 250. The metal film 280 can be formedsimultaneously with formation of a source line 254 and a drain line 260.As the metal film 280, a film mainly containing Al or Ag that is thesame material as that of the lines, or a material having excellentreflectivity such as a compound film thereof is desirably used.

[0395] Light is radiated to a subject 270 from an EL element, and lightreflected form the subject 270 is radiated to the photodiode 306.However, in this case, among light passing through the photodiode 306,there exists light that is not radiated to a photoelectric conversionlayer 248. If the metal film 280 is present as shown in FIG. 16, suchlight is reflected from the metal film 280, whereby the photoelectricconversion layer 248 can receive it. Because of this, the photoelectricconversion layer 248 can receive more light.

[0396] In this embodiment, Embodiments 1 to 7 can be arbitrarilycombined.

[0397] Embodiment 9

[0398] In this embodiment, an exemplary EL display apparatus(light-emitting apparatus) produced according to the present inventionwill be described with reference to FIGS. 17A-17B and 18A-18C.

[0399]FIG. 17A is a top view of a TFT substrate of an EL displayapparatus of the present invention. In the present specification, theTFT substrate refers to the one on which a pixel portion is provided.

[0400] A pixel portion 4002, a source signal line driving circuit 4003 afor a sensor, a source signal line driving circuit 4003 b for an ELelement, a gate signal line driving circuit 4004 a for an EL element,and a gate signal line driving circuit 4004 b for a sensor are providedon a substrate 4001. According to the present invention, the number ofthe source signal line driving circuits and the gate signal line drivingcircuits are not limited to those shown in FIG. 17A. The number of thesource signal line driving circuits and the gate signal line drivingcircuits can be appropriately set by a designer. In this embodiment,although the source signal line driving circuits and the gate signalline driving circuits are provided on the TFT substrate, the presentinvention is not limited thereto. The source signal line drivingcircuits and the gate signal line driving circuits provided on asubstrate separate from the TFT substrate may be electrically connectedto the pixel portion via FPCs or the like.

[0401] Reference numeral 4005 denotes drawing-around wiring connected toa power supply line (not shown) provided in the pixel portion 4002.Reference numeral 4005 also denotes drawing-around wiring for a gateconnected to the gate signal line driving circuit 4004 a for a sensorand the gate signal line driving circuit 4004 b for a gate. Referencenumeral 4005 also denotes drawing-around wiring for a source connectedto the source signal line driving circuit 4003 a for a sensor and thesource signal line driving circuit 4003 b for an EL element.

[0402] The drawing-around wiring 4005 for a gate and the drawing-aroundwiring 4005 for a source are connected to an IC and the like providedoutside of the substrate 4001 via the FPCs 4006. The drawing-aroundwiring 4005 is also connected to a power source provided outside of thesubstrate 4001 via the FPCs 4006.

[0403]FIG. 17B shows an enlarged view of the drawing-around wiring 4005.Reference numeral 4100 denotes drawing-around wiring for R, 4101 denotesdrawing-around wiring for G, and 4102 denotes drawing-around wiring forB.

[0404]FIG. 18A shows a top view of an area sensor formed by sealing theTFT substrate shown in FIG. 17A with a sealant. FIG. 18B shows across-sectional view taken along a line A-A′ in FIG. 18A, and FIG. 18Cshows a cross-sectional view taken along a line B-B′ in FIG. 18A. Thesame components as those shown in FIGS. 17A and 17B are denoted with thesame reference numerals as those therein.

[0405] A sealant 4009 is provided so as to surround the pixel portion4002, the source signal line driving circuit 4003 a for a sensor, thesource signal line driving circuit 4003 b for an EL element, the gatesignal line driving circuit 4004 a for a sensor, and the gate signalline driving circuit 4004 b for an EL element formed on the substrate4001. Furthermore, a sealing member 4008 is provided above the pixelportion 4002, the source signal line driving circuit 4003 a for asensor, the source signal line driving circuit 4003 b for an EL element,the gate signal line driving circuit 4004 a for a sensor, and the gatesignal line driving circuit 4004 b for an EL element. Thus, the pixelportion 4002, the source signal line driving circuit 4003 a for asensor, the source signal line driving circuit 4003 b for an EL element,the gate signal line driving circuit 4004 a for a sensor, and the gatesignal line driving circuit 4004 b for an EL element are sealed with thesubstrate 4001, the sealant 4009, and the sealing member 4008, using afiller 4210.

[0406] Furthermore, the pixel portion 4002, the source signal linedriving circuit 4003 a for a sensor, the source signal line drivingcircuit 4003 b for an EL element, the gate signal line driving circuit4004 a for a sensor, and the gate signal line driving circuit 4004 b foran EL element provided on the substrate 4001 have a plurality of TFTs.FIG. 18B typically shows driving TFTs (herein, an N-channel type TFT anda P-channel type TFT are shown) 4201 included in the source signal linedriving circuit 4003, and an EL driving TFT (i.e., TFT for controlling acurrent to an EL element) and a photodiode 4211 included in the pixelportion, formed on a base film 4010.

[0407] In this embodiment, as the driving TFT 4201, a P-channel type TFTor an N-channel type TFT produced by a known method is used. As the ELdriving TFT 4202, a P-channel type TFT produced by a known method isused. Furthermore, in the pixel portion 4002, a retention capacitance(not shown) connected to a gate of the EL driving TFT 4202 is provided.

[0408] An interlayer insulating film (flattening film) 4301 is formed onthe driving TFT 4201, the EL driving TFT 4202, and the photodiode 4211.A pixel electrode (positive electrode) 4203 electrically connected to adrain of the EL driving TFT 4202 is formed on the interlayer insulatingfilm 4301. As the pixel electrode 4203, a transparent conductive filmwith a large work function is used. As the transparent conductive film,a compound of indium oxide and tin oxide, a compound of indium oxide andzinc oxide, zinc oxide, tin oxide, or indium oxide can be used.Furthermore, gallium may be added to the transparent conductive film.

[0409] On the pixel electrode 4203, an insulating film 4302 is formed.The insulating film 4302 has an opening in a portion corresponding tothe pixel electrode 4203. In this opening, an EL layer 4204 is formed onthe pixel electrode 4203. As the EL layer 4204, a known organic ELmaterial or an inorganic EL material can be used. There are alow-molecular type (monomer type) material and a high-molecular type(polymer type) material as the organic EL material. Either material maybe used.

[0410] The EL layer 4204 may be formed by a known vapor depositiontechnique or a coating technique. Furthermore, the EL layer may have amulti-layer configuration or a single-layer configuration by arbitrarilycombining a hole injection layer, a hole transport layer, alight-emitting layer, an electron transport layer, or an electroninjection layer.

[0411] On the EL layer 4204, a negative electrode 4205 made of aconductive film (typically, conductive film mainly containing aluminum,copper, or silver, or a layered film composed of this conductive filmand another conductive film) having a light shielding property isformed. Furthermore, it is desirable to exclude moisture and oxygenpresent on an interface between the negative electrode 4205 and the ELlayer 4204 as much as possible. Thus, it is required to form the ELlayer 4204 in an atmosphere of nitrogen or noble gas, and to form thenegative electrode 4205 without bringing it into contact with oxygen andmoisture. In this embodiment, the above-mentioned film-formation ispossible by using a film-formation apparatus of a multi-chamber system(cluster-tool system). The negative electrode 4205 is supplied with apredetermined voltage.

[0412] As described above, an EL element 4303 composed of the pixelelectrode (positive electrode) 4203, the EL layer 4204, and the negativeelectrode 4205 is formed. Then, a protective film 4209 is formed on theinsulating film 4302 so as to cover the EL element 4303. The protectivefilm 4209 is effective for preventing oxygen, moisture, and the likefrom entering the EL element 4303.

[0413] Reference numeral 4005 denotes drawing-around wiring connected toa power supply line, which is electrically connected to a source regionof the EL driving TFT 4202. The drawing-around wiring 4005 extendsbetween the sealant 4009 and the substrate 4001, and is electricallyconnected to wiring 4301 of the FPCs via an anisotropic conductive film4300.

[0414] As the sealing member 4008, a glass material, a metal material(typically, a stainless material), a ceramics material, and a plasticmaterial (including a plastic film) can be used. As the plasticmaterial, a fiberglass-reinforced plastic (FRP) plate, a polyvinylfluoride film (PVF), a myler film, a polyester film, or an acrylic resinfilm can be used. Furthermore, a sheet having a configuration in whichan aluminum foil is interposed between a PVF film and a myler film canalso be used.

[0415] In the case where light is radiated from an EL element toward acover member side, the cover member must be transparent. In this case, atransparent material, such as a glass plate, a plastic plate, apolyester film, or an acrylic film, is used for the cover member.

[0416] As the filler 4210, UV-curable resin or thermosetting resin, aswell as inert gas such as nitrogen and argon, can be used. Morespecifically, polyvinyl chloride (PVC), acrylic resin, polyimide, epoxyresin, silicon resin, polyvinyl butyral (PVB), or ethylenevinyl acetate(EVA) can be used. In this embodiment, nitrogen is used as the filler.

[0417] In order to expose the filler 4210 to a moisture-absorbingmaterial (preferably, barium oxide) or an oxygen-adsorbing material, aconcave portion 4007 is provided on the surface of the sealing member4008 on the substrate 4001 side, and a moisture-absorbing material or anoxygen-adsorbing material 4207 is disposed therein. Themoisture-absorbing material or oxygen-adsorbing material 4207 is held inthe concave portion 4007 by a concave portion cover member 4208 so asnot to scatter. The concave portion cover member 4208 has a fine meshshape which transmits air and moisture but does not transmit themoisture-absorbing material or the oxygen-adsorbing material 4207. Byproviding the moisture-absorbing material or the oxygen-adsorbingmaterial 4207, the EL element 4303 can be prevented from being degraded.

[0418] As shown in FIG. 18C, a conductive film 4203 a is formed so as tocome into contact with the drawing-around wiring 4005 a, simultaneouslywith the formation of the pixel electrode 4203.

[0419] Furthermore, the anisotropic conductive film 4300 contains aconductive filler 4300 a. By thermally crimping the substrate 4001 ontothe FPC 4006, the conductive film 4203 a on the substrate 4001 and thewiring 4301 for an FPC on the FPC 4006 are electrically connected toeach other via the conductive filler 4300 a.

[0420] In this embodiment, Embodiments 1 to 7 can be arbitrarilycombined.

[0421] Embodiment 10

[0422] In this embodiment, the case will be described with reference toFIGS. 19A to 19C, in which TFTs and EL elements are sealed onto asubstrate with a sealing member, and thereafter, the substrate isreplaced. FIGS. 19A to 19C are cross-sectional views showing the stepsof producing a pixel portion.

[0423] In FIG. 19A, reference numeral 3101 denotes a substrate(hereinafter, referred to as a “device forming substrate”) on whichdevices are to be formed. On the substrate 3101, a peeling layer 3102made of an amorphous silicon film is formed to a thickness of 100 to 500nm (300 nm in this embodiment). In this embodiment, although a glasssubstrate is used as the device forming substrate 3101, a quartzsubstrate, a silicon substrate, a metal substrate (SUS substrate), or aceramic substrate may be used.

[0424] The peeling layer 3102 may be formed by thermal CVD under reducedpressure, plasma CVD, sputtering, or vapor deposition. On the peelinglayer 3102, an insulating film 3103 is made of a silicon oxide filmhaving a thickness of 200 nm. The insulating film 3103 may be formed bythermal CVD under reduced pressure, plasma CVD, sputtering, or vapordeposition.

[0425] Furthermore, photodiodes 3104 and EL driving TFTs 3105 are formedon the insulating film 3103. In this embodiment, although the EL drivingTFTs 3105 are P-channel type TFTs, the present invention is not limitedthereto. The EL driving TFTs 3105 may be P-channel type TFTs orN-channel type TFTs.

[0426] A first interlayer insulating film 3107 is formed on thephotodiodes 3104 and the EL driving TFTs 3105. The first interlayerinsulating film 3107 is formed covering the photodiodes 3104 and the ELdriving TFTs 3105, so as to flatten pixel electrodes 3106 (formedlater).

[0427] Each pixel electrode 3106 is formed so as to be electricallyconnected to a drain region of the EL driving TFT 3105. In thisembodiment, the pixel electrode 3106 is obtained by forming atransparent conductive film (typically, a compound film of indium oxideand tin oxide) having a thickness of 100 nm, followed by patterning. Thepixel electrode 3106 functions as a positive electrode of an EL element.

[0428] After the pixel electrodes 3106 are formed, a second interlayerinsulating film 3114 made of a silicon oxide film with a thickness of300 nm is formed. Openings 3108 are formed in the second interlayerinsulating film 3114, and EL layers 3109 with a thickness of 70 nm and anegative electrode 3110 with a thickness of 300 nm are formed by vapordeposition. In this embodiment, the EL layer 3109 has a configuration inwhich a hole injection layer with a thickness of 20 nm and alight-emitting layer with a thickness of 50 nm are stacked. Needless tosay, another known configuration may be used in which a hole-injectionlayer, a hole transport layer, an electron transport layer, or anelectron injection layer are combined with a light-emitting layer.

[0429] As described above, an EL element 3111 composed of the pixelelectrode (positive electrode) 3106, the EL layer 3109, and the negativeelectrode 3110 is obtained. In this embodiment, the EL element 3111functions as a light-emitting element.

[0430] Next, a substrate (hereinafter, referred to as a “sealingmember”) 3113 for fixing the devices is attached to the layeredconfiguration obtained as described above with a first adhesive 3112. Inthis embodiment, although an elastic plastic film is used as the sealingmember 3113, a glass substrate, a quartz substrate, a plastic substrate,a silicon substrate, or a ceramic substrate may be used. As the firstadhesive 3112, it is required to use a material that can allow thepeeling layer 3102 to be selectively removed later.

[0431] Typically, an insulating film made of resin can be used. In thisembodiment, although polyimide is used, acrylic resin, polyamide, orepoxy resin may be used. If the adhesive 3112 is positioned on a side ofan observer (i.e., on a side of a user of an electrooptical apparatus)seen from the EL elements, a material that transmits light needs to beused.

[0432] The first adhesive 3112 can shut off the EL elements from theatmosphere. This can substantially completely suppress the degradationof an organic EL material due to oxidation, and the reliability of theEL elements can be substantially enhanced.

[0433] Next, as shown in FIG. 19B, the peeling layer 3102 is removed,whereby the device forming substrate 3101 and the insulating film 3103are peeled off. In this embodiment, peeling is conducted by exposing thepeeling layer 3102 to gas containing halogen fluoride. In thisembodiment, chloride fluoride (ClF₃) is used as halogen fluoride, andnitrogen is used as diluted gas. As the diluted gas, argon, helium, orneon may be used. The flow rate of ClF₃ and nitrogen may be set at 500sccm (8.35×10⁻⁶ m³/s), and a reaction pressure thereof may be set at 1to 10 Torr (1.3×10² to 1.3×10³ Pa). Furthermore, a treatment temperaturemay be a room temperature (typically, 20° C. to 27° C.).

[0434] In the above-mentioned case, although a silicon film is etched, aplastic film, a glass substrate, a polyimide film, and a silicon oxidefilm are not etched. More specifically, the peeling layer 3102 isselectively etched by being exposed of ClF₃ gas, and finally removedcompletely. The active layers of the photodiode 3104 and the EL drivingTFT 3105 similarly formed of a silicon film are covered with the firstinterlayer insulating film 3107. Therefore, they are not exposed to ClF₃gas and hence, are not etched.

[0435] In the case of this embodiment, the peeling layer 3102 isgradually etched from exposed ends. When the peeling layer 3102 isremoved completely, the device forming substrate 3101 and the insulatingfilm 3103 are separated. At this time, the TFTs and EL elements formedof stacked thin films remain on the side of the sealing member 3113.

[0436] Herein, the peeling layer 3102 is etched from the ends thereof.When the device forming substrate 3101 is increased in size, it takes alonger time for the peeling layer 3102 to be completely removed, whichis not preferable. Thus, the peeling layer 3102 is removed by etching,desirably when the device forming substrate 3101 has a size of 3 inchesor less (preferably, one inch or less), measured from the upper leftcorner to the lower right comer.

[0437] In this embodiment, the peeling layer 3102 is removed by etchingin an atmosphere of ClF₃ gas. The present invention is not limitedthereto. It may also be possible that a laser beam is radiated to thepeeling layer 3102 from the device forming substrate 3101 side tovaporize the peeling layer 3102, whereby the device forming substrate3101 is peeled off. In this case, it is required to appropriately selectthe kind of a laser beam and the material for the device formingsubstrate 3101 so that a laser beam passes through the device formingsubstrate 3101. For example, when a quartz substrate is used as thedevice forming substrate 3101, a YAG laser (fundamental (1064 nm),second harmonic (532 nm), third harmonic (355 nm), fourth harmonic (266nm)) or an excimer laser (wavelength: 308 nm) is used to form aline-shaped beam and the line-shaped beam may be allowed to pass throughthe quartz substrate. An excimer laser does not pass through a glasssubstrate. Therefore, if a glass substrate is used as the device formingsubstrate 3101, a fundamental, a second harmonic, and a third harmonicof the YAG laser (preferably, the second harmonic (wavelength: 532 nm))is used to form a line-shaped beam, and the line-shaped beam may beallowed to pass through a glass substrate.

[0438] In the case of conducting peeling by using a laser beam, thepeeling layer 3102 that is vaporized with a laser beam to be radiated isused.

[0439] In addition to the method of using a laser beam, it may also bepossible that the device forming substrate 3101 is peeled off bydissolving the peeling layer 3102 in a solution. In this case, it ispreferable to use a solution that allows the peeling layer 3102 to beselectively dissolved.

[0440] When the TFTs and the EL elements are transferred to the sealingmember 3113, as shown in FIG. 19C, a second adhesive 3114 is formed, anda second device forming substrate 3115 is attached. As the secondadhesive 3114, an insulating film made of resin (typically, polyimide,acrylic resin, polyamide, or epoxy resin) may be used. Alternatively, aninorganic insulating film (typically, a silicon oxide film) may be used.In the case where the second adhesive 3114 is positioned on an observerside, seen from the EL elements, a material transmitting light needs tobe used.

[0441] As described above, the TFTs and the EL elements are transferredfrom the device forming substrate 3101 to the second device formingsubstrate 3115. Consequently, an EL display apparatus interposed betweenthe sealing member 3113 and the second device forming substrate 3115 canbe obtained. If the sealing member 3113 and the second device formingsubstrate 3115 are made of the same material, thermal expansioncoefficients thereof become equal to each other. Therefore, theapparatus becomes unlikely to be influenced by stress distortion due toa change in temperature.

[0442] In the EL display apparatus produced in this embodiment, thematerial for the sealing member 3113 and the second device formingsubstrate 3115 can be selected without being influenced by heatresistance during a process of TFTs. For example, a plastic substratecan be used as the sealing member 3113 and the second device formingsubstrate 3115, whereby a flexible EL display apparatus can be created.

[0443] This embodiment can be carried out by being arbitrarily combinedwith any of the configurations shown in Embodiments 1 to 8.

[0444] Embodiment 11

[0445] In this embodiment, the case will be described in which a DLCfilm is formed over the entire surface of an EL display apparatus or atends of an EL display apparatus.

[0446]FIG. 20A is a cross-sectional view of an EL display apparatus inwhich a DLC film is formed over the entire surface of the apparatus. Ona substrate 3201, a switching TFT 3205, an EL driving TFT 3204, and aphotodiode 3206 are formed. Reference numeral 3203 denotes an ELelement. The EL driving TFT 3204 controls a current flowing through theEL element 3203.

[0447] The switching TFT 3205, the EL driving TFT 3204, and the ELelement 3203 are sealed with a sealing member 3202 and a sealant 3208 soas to be shut off from outside air. Reference numeral 3209 denotesdrawing-around wiring. The drawing-around wiring 3209 extends betweenthe sealant 3208 and the substrate 3201, and is exposed to the outsideof the space in which the EL element 3203 is sealed.

[0448] Reference numeral 3210 denotes a DLC film. The DLC film 3210covers the entire EL display apparatus, excluding a part of thedrawing-around wiring 3209 exposed to the outside of the space in whichthe EL element 3203 is sealed.

[0449] In this embodiment, a DLC film may be formed by ECR plasma CVD,RF plasma CVD, μ-wave plasma CVD, or sputtering. The DLC film has aRaman spectrum distribution with an asymmetric peak at about 1550 cm⁻¹and a shoulder at about 1300 cm⁻¹. The DLC film also exhibits a hardnessof 15 to 25 GPa, when measured by minute hardness meter. Such a carbonfilm protects the surface of a substrate. In particular, a plasticsubstrate is likely to be damaged. Therefore, covering the surface ofthe apparatus with a DLC film as shown in FIG. 20A is effective forpreventing damage.

[0450] The DLC film is also effective for preventing oxygen and waterfrom entering the space in which the EL element 3203 is sealed. Thus, byforming the DLC film 3210 so as to cover the sealant 3208 as in thisembodiment, a material promoting the degradation of an EL layer, such asmoisture and oxygen, from outside can be prevented from entering thespace in which the EL element 3203 is sealed.

[0451] When the DLC film 3210 is formed, a part of the drawing-aroundwiring 3209 exposed to the outside of the space in which the EL element3203 is sealed is covered with a resist mask or the like, and the resistmask is removed after the DLC film 3210 is formed. A part of thedrawing-around wiring 3209 not covered with the DLC film 3210 isconnected to wiring 3212 for an FPC provided at an FPC 3211 via ananisotropic conductive film 3213.

[0452]FIG. 20B is a cross-sectional view of an EL display apparatus inthe case where a DLC film is formed at ends of the EL display apparatus.On a substrate 3301, a switching TFT 3305, an EL driving TFT 3304, and aphotodiode 3306 are formed. Reference numeral 3303 denotes an ELelement, and the EL driving TFT 3304 controls a current flowing throughan EL element 3303.

[0453] The switching TFT 3305, the EL driving TFT 3304, the photodiode3306, and the EL element 3303 are sealed with a sealing member 3302 anda sealant 3308 so as to be shut off from outside air. Reference numeral3309 denotes drawing-around wiring. The drawing-around wiring 3309extends between the sealant 3308 and the substrate 3301, and the ELelement 3303 is exposed to the outside of the space in which the ELelement 3303 is sealed.

[0454] Reference numeral 3310 denotes a DLC film. The DLC film 3310 isformed so as to cover a part of the sealing member 3302, a part of thesubstrate 3301, and the sealant 3308, excluding a part of thedrawing-around wiring 3309 exposed to the outside of the space in whichthe EL element 3303 is sealed.

[0455] The DLC film 3310 is effective for preventing oxygen and waterfrom entering the space in which the EL element 3303 is sealed. Thus, byforming the DLC film 3310 so as to cover the sealant 3308 as in thisembodiment, a material promoting the degradation of an EL layer, such asmoisture and oxygen, from outside can be prevented from entering thespace in which the EL element 3303 is sealed.

[0456] In an EL display apparatus shown in FIG. 20B, the DLC film 3310is formed only at ends (portions including the sealant) of the ELdisplay apparatus. Therefore, it is easy to form the DLC film 3310.

[0457] When the DLC film 3310 is formed, a part of the drawing-aroundwiring 3309 exposed to the outside of the space in which the EL element3303 is sealed is covered with a resist mask or the like, and the resistmask is removed after the DLC film 3310 is formed. A part of thedrawing-around wiring 3309 not covered with the DLC film 3310 isconnected to wiring 3312 for an FPC provided at an FPC 3311 via ananisotropic conductive film 3313.

[0458] This embodiment can be carried out by being arbitrarily combinedwith any of the configurations shown in Embodiments 1 to 10.

[0459] Embodiment 12

[0460] As an exemplary area sensor of the present invention, a portablehand scanner will be described with reference to FIGS. 21A and 21B.

[0461]FIG. 21A shows a portable hand scanner, which is composed of abody 401, a sensor portion 402, an upper cover 403, an externalconnecting port 404, and operation switches 405. FIG. 21B shows a statewhere the upper cover 403 of the portable hand scanner in FIG. 21A isclosed.

[0462] The area sensor of the present invention is capable of displayinga read image on the sensor portion 402. Therefore, even if an electronicdisplay is not separately provided to the area sensor, an image can beconfirmed as soon as it is read.

[0463] The area sensor of the present invention is also capable ofsending an image signal read by the sensor portion 402 to electronicequipment connected to the outer side of the portable hand scannerthrough the external connecting port 404, whereby the image iscorrected, synthesized, edited, and the like on software.

[0464] This embodiment can be arbitrarily combined with any ofEmbodiments 1 to 11.

[0465] Embodiment 13

[0466] As an exemplary area sensor of the present invention, a portablehand scanner different from that of Embodiment 12 will be described withreference to FIG. 22.

[0467] Reference numeral 501 denotes a sensor substrate, 502 denotes asensor portion, 503 denotes a touch panel, and 504 denotes a touch pen.The touch panel 503 has light transparency. Because of this, the touchpanel 503 can transmit light emitted from the sensor portion 502 andlight incident upon the sensor portion 502, and an image on a subjectcan be read through the touch panel 503. In the case where an image isdisplayed on the sensor portion 502, an image on the sensor portion 502can be seen through the touch panel 503.

[0468] When the touch pen 504 contacts the touch panel 503, informationat a position where the touch pen 504 is in contact with the touch panel503 can be captured in an area sensor as an electric signal. As thetouch panel 503 and the touch pen 504 used in this embodiment, any knownmembers can be used, as long as the touch panel 503 has lighttransparency, and information at a position where the touch pen 504contacts the touch panel 503 can be captured in an area sensor as anelectric signal.

[0469] The area sensor of the present invention having theabove-mentioned configuration is capable of reading an image, displayingthe read image on the sensor portion 502, and writing to the capturedimage with the touch pen 504. In the area sensor of the presentinvention, read of an image, display of an image, write to an image canbe all conducted in the sensor portion 502. Thus, the size of the areasensor can be minimized, and the area sensor is allowed to have variousfunctions.

[0470] This embodiment can be arbitrarily combined with any ofEmbodiments 1 to 12.

[0471] Embodiment 14

[0472] In this embodiment, a configuration of a sensor portion of anarea sensor will be described, which is different from that shown inFIG. 1.

[0473]FIG. 24 shows a circuit diagram of a sensor portion of an areasensor of this embodiment. A sensor portion 1001 is provided with sourcesignal lines S₁ to S_(x), power supply lines V₁ to V_(x), gate signallines G₁ to G_(y), reset gate signal lines RG₁ to RG_(y), sensor outputlines SS₁ to SS_(x), and a sensor power source line VB.

[0474] The sensor portion 1001 has a plurality of pixels 1002. Eachpixel 1002 includes one of the source signal liens S₁ to S_(x), one ofpower supply lines V₁ to V_(x), one of gate signal lines G₁ to G_(y),one of reset gate signal lines RG₁ to RG_(y), one of sensor output linesSS₁ to S^(x), and the sensor power source line VB.

[0475] The sensor output lines SS₁ to SS_(x) are respectively connectedto constant current power sources 1003 _(—1) to 1003 _(—x).

[0476] The pixel 1002 includes a switching TFT 1004, an EL driving TFT1005, and an EL element 1006. In FIG. 24, although a capacitor 1007 isprovided in the pixel 1002, the capacitor 1007 may not be provided. Thepixel 1002 further includes a reset TFT 1010, a buffer TFT 1011, aselective TFT 1012, and a photodiode 1013.

[0477] The EL element 1006 is composed of a positive electrode, anegative electrode, and an EL layer provided between the positiveelectrode and the negative electrode. In the case where the positiveelectrode is connected to a source region or a drain region of the ELdriving TFT 1005, the positive electrode functions as a pixel electrodeand the negative electrode functions as a counter electrode. Incontrast, in the case where the negative electrode is connected to asource region or a drain region of the EL driving TFT 1005, the positiveelectrode functions as a counter electrode and the negative electrodefunctions as a pixel electrode.

[0478] A gate electrode of the switching TFT 1004 is connected to thegate signal line (G₁ to G_(y)). One of a source region and a drainregion of the switching TFT 1004 is connected to the source signal line(S₁ to S_(x)), and the other is connected to the gate electrode of theEL driving TFT 1005.

[0479] One of the source region and the drain region of the EL drivingTFT 1005 is connected to the power supply line (V₁ to V_(x)), and theother is connected to the EL element 1006. The capacitor 1007 isprovided so as to be connected to the gate electrode of the EL drivingTFT 1005 and the power supply line (V₁ to V_(x)).

[0480] A gate electrode of the reset TFr 1010 is connected to the resetgate signal line (RG₁ to RG_(x)). A source region of the reset TFT 1010is connected to the sensor power source line VB. The sensor power sourceline VB is always kept at a constant electric potential (referencepotential). A drain region of the reset TFT 1010 is connected to thephotodiode 1013 and a gate electrode of the buffer TFT 1011.

[0481] Although not shown in the figure, the photodiode 1013 has anN-type semiconductor layer, a P-type semiconductor layer, and aphotoelectric conversion layer provided between the N-type semiconductorlayer and the P-type semiconductor layer. The drain region of the resetTFT 1010 is connected to either the P-type semiconductor layer or theN-type semiconductor layer of the photodiode 1013.

[0482] A drain region of the buffer TFT 1011 is connected to the sensorpower source line VB, and is always kept at a constant referencepotential. A source region of the buffer TFT 1011 is connected to asource region or a drain region of the selective TFT 1012.

[0483] A gate electrode of the selective TFT 1012 is connected to thegate signal line (G₁ to G_(x)). One of a source region and a drainregion of the selective TFT 1012 is connected to the source region ofthe buffer TFT 1011 as described above, and the other is connected tothe sensor output line (SS₁ to SS_(x)). The sensor output line (SS₁ toSS_(x)) is connected to the constant current power source (103 _(—1) to103 _(—x)), and is always supplied with a constant current.

[0484] In this embodiment, the polarity of the switching TFT 1004 is thesame as that of the selective TFT 1012. That is, when the switching TFT1004 is an N-channel type TFT, the selective TFT 1012 is also anN-channel type TFT. When the switching TFT 1004 is a P-channel type TFT,the selective TFT 1012 is also a P-channel type TFT.

[0485] Unlike the area sensor shown in FIG. 1, in the sensor portion ofthe area sensor of this embodiment, a gate electrode of the switchingTFT 1004 and a gate electrode of the selective TFT 1012 are bothconnected to the gate signal lines (G₁ to G_(x)). Therefore, in the caseof the area sensor of this embodiment, the length of a period duringwhich the EL element 1006 of each pixel emits light is the same as thatof a sampling period (ST₁ to ST_(N)). Because of the above-mentionedconfiguration, the number of wirings can be decreased in the area sensorof this embodiment, compared with the case shown in FIG. 1.

[0486] The area sensor of this embodiment is also capable of displayingan image on the sensor portion 1001.

[0487] The configuration of this embodiment can be arbitrarily combinedwith any of Embodiments 1 to 13.

[0488] Embodiment 15

[0489] Examples of electronic equipment using an area sensor of thepresent invention include a video camera, a digital still camera, anotebook computer, a portable information terminal (mobile computer,mobile phone, portable game machine, electronic book, etc.), and thelike.

[0490]FIG. 25A shows a video camera, which includes a body 2101, adisplay portion 2102, an image receiving portion 2103, an operation key2104, an external connecting port 2105, a shutter 2106 and the like. Thearea sensor of the present invention can be applied to the displayportion 2102.

[0491]FIG. 25B shows a mobile computer, which includes a body 2301, adisplay portion 2302, a switch 2303, operation keys 2304, an infraredport 2305, and the like. The area sensor of the present invention can beapplied to the display portion 2302.

[0492]FIG. 25C shows a mobile phone, which includes a body 2701, ahousing 2702, a display portion 2703, a voice input portion 2704, avoice output portion 2705, operation keys 2706, an external connectingportion 2707, an antenna 2708, and the like. The area sensor of thepresent invention can be applied to the display portion 2703.

[0493] As described above, the application range of the presentinvention is very large. Thus, the present invention can be used forelectronic equipment in various fields.

[0494] This embodiment can be arbitrarily combined with the embodiment,and any of Embodiments 1 to 14.

[0495] According to the present invention, due to the above-mentionedconfiguration, light is radiated uniformly to a subject, so that noinconsistencies in lightness are caused in a read image. Furthermore,unlike a conventional example, it is not required to provide a backlightand a light scattering plate separately from a sensor substrate.Therefore, the mechanical strength of an area sensor is increasedwithout requiring precise adjustment of the position of a backlight, alight scattering plate, a sensor substrate, and a subject. As a result,an area sensor can be made small, thin, and light-weight.

[0496] The area sensor of the present invention is also capable ofdisplaying an image on a sensor portion, using EL elements. Therefore,even if an electronic display is not separately provided to the areasensor, an image read by the sensor portion can be displayed on thesensor portion, and the read image can be confirmed immediately.

[0497] Furthermore, in a photodiode used in the present invention, aphotoelectric conversion layer is made of an amorphous silicon film, anN-type semiconductor layer is made of an N-type polycrystalline siliconfilm, and a P-type semiconductor layer is made of a P-typepolycrystalline silicon film. The amorphous silicon film is thicker thanthe polycrystalline silicon film, and the ratio in thicknesstherebetween is preferably (1 to 10):1. Since the amorphous silicon filmis thicker than the polycrystalline silicon film, the photoelectricconversion layer can receive more light. According to the presentinvention, the amorphous silicon film has a light absorptivity higherthan that of the polycrystalline silicon film and the like, so that anamorphous silicon film is used for the photoelectric conversion layer.

[0498] Various other modifications will be apparent to and can bereadily made by those skilled in the art without departing from thescope and spirit of this invention. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the description asset forth herein, but rather that the claims be broadly construed.

What is claimed is:
 1. An area sensor comprising a sensor portion, thesensor portion comprising: a plurality of pixels, each of the pluralityof pixels comprising a photodiode, an electroluminescence element and aplurality of thin film transistors, wherein the photodiode includes aphotoelectric conversion layer that is in contact with a part of aP-type semiconductor layer and an N-type semiconductor layer and is madeof an amorphous semiconductor film and the photoelectric conversionlayer is thicker than the P-type semiconductor layer and the N-typesemiconductor layer.
 2. An area sensor comprising a sensor portion, thesensor portion comprising: a plurality of pixels, each of the pluralityof pixels comprising a photodiode, an electroluminescence element and aplurality of thin film transistors, wherein a light emitted from theelectroluminescence element is reflected from a subject to be radiatedto the photodiode, the photodiode generates an image signal from thelight radiated to the photodiode, the photodiode includes aphotoelectric conversion layer that is in contact with a part of aP-type semiconductor layer and an N-type semiconductor layer and is madeof an amorphous semiconductor film and the photoelectric conversionlayer is thicker than the P-type semiconductor layer and the N-typesemiconductor layer.
 3. An area sensor comprising a sensor portion, thesensor portion comprising: a plurality of pixels, each of the pluralityof pixels comprising a photodiode, an electroluminescence element and aplurality of thin film transistors, wherein the plurality of thin filmtransistors control light emission of the electroluminescence element, alight emitted from the electroluminescence element is reflected from asubject to be radiated to the photodiode, the photodiode and theplurality of thin film transistors generate an image signal from thelight radiated to the photodiode, the photodiode includes aphotoelectric conversion layer that is in contact with a part of aP-type semiconductor layer and an N-type semiconductor layer and is madeof an amorphous semiconductor film and the photoelectric conversionlayer is thicker than the P-type semiconductor layer and the N-typesemiconductor layer.
 4. An area sensor comprising a sensor portion, thesensor portion comprising: a plurality of pixels, each of the pluralityof pixels comprising a photodiode, an electroluminescence element and aplurality of thin film transistors, wherein the pixel includes aphotodiode, an electroluminescence element, a switching TFT, anelectroluminescence driving TFT, a reset TFT, a buffer TFT and aselective TFT, the switching TFT and the electroluminescence driving TFTcontrol light emission of the electroluminescence element, light emittedfrom the electroluminescence element is reflected from a subject to beradiated to the photodiode, the photodiode and the plurality of thinfilm transistors generate an image signal from the light radiated to thephotodiode, the photodiode includes a photoelectric conversion layerthat is in contact with a part of a P-type semiconductor layer and anN-type semiconductor layer and is made of an amorphous semiconductorfilm and the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.
 5. An areasensor according to claim 1, wherein the N-type semiconductor layercomprises polysilicon.
 6. An area sensor according to claim 2, whereinthe N-type semiconductor layer comprises polysilicon
 7. An area sensoraccording to claim 3, wherein the N-type semiconductor layer comprisespolysilicon
 8. An area sensor according to claim 4, wherein the N-typesemiconductor layer comprises polysilicon
 9. An area sensor according toclaim 1, wherein the P-type semiconductor layer comprises polysilicon.10. An area sensor according to claim 2, wherein the P-typesemiconductor layer comprises polysilicon
 11. An area sensor accordingto claim 3, wherein the P-type semiconductor layer comprises polysilicon12. An area sensor according to claim 4, wherein the P-typesemiconductor layer comprises polysilicon
 13. An area sensor accordingto claim 1, wherein the electric conversion layer comprises amorphoussilicon.
 14. An area sensor according to claim 2, wherein the electricconversion layer comprises amorphous silicon.
 15. An area sensoraccording to claim 3, wherein the electric conversion layer comprisesamorphous silicon.
 16. An area sensor according to claim 4, wherein theelectric conversion layer comprises amorphous silicon.
 17. An areasensor according to claim 1, wherein the electroluminescence element hasa positive electrode, a negative electrode and an electroluminescencelayer provided between the positive electrode and the negativeelectrode.
 18. An area sensor according to claim 2, wherein theelectroluminescence element has a positive electrode, a negativeelectrode and an electroluminescence layer provided between the positiveelectrode and the negative electrode.
 19. An area sensor according toclaim 3, wherein the electroluminescence element has a positiveelectrode, a negative electrode and an electroluminescence layerprovided between the positive electrode and the negative electrode. 20.An area sensor according to claim 4, wherein the electroluminescenceelement has a positive electrode, a negative electrode and anelectroluminescence layer provided between the positive electrode andthe negative electrode.
 21. An area sensor according to claim 1, whereinan electronic equipment using the area sensor is an equipment, which isselected from the group of a video camera, a digital still camera, anotebook computer and a portable information terminal.
 22. An areasensor according to claim 2, wherein an electronic equipment using thearea sensor is an equipment, which is selected from the group of: avideo camera, a digital still camera, a notebook computer and a portableinformation terminal.
 23. An area sensor according to claim 3, whereinan electronic equipment using the area sensor is an equipment, which isselected from the group of: a video camera, a digital still camera, anotebook computer and a portable information terminal.
 24. An areasensor according to claim 4, wherein an electronic equipment using thearea sensor is an equipment, which is selected from the group of: avideo camera, a digital still camera, a notebook computer and a portableinformation terminal.
 25. A display apparatus comprising a sensorportion, the sensor portion comprising: a plurality of pixels, each ofthe plurality of pixels comprising a photodiode, an electroluminescenceelement and a plurality of thin film transistors, wherein the photodiodeincludes a photoelectric conversion layer that is in contact with a partof a P-type semiconductor layer and an N-type semiconductor layer and ismade of an amorphous semiconductor film and the photoelectric conversionlayer is thicker than the P-type semiconductor layer and the N-typesemiconductor layer.
 26. A display apparatus comprising a sensorportion, the sensor portion comprising: a plurality of pixels, each ofthe plurality of pixels comprising a photodiode, an electroluminescenceelement and a plurality of thin film transistors, wherein a lightemitted from the electroluminescence element is reflected from a subjectto be radiated to the photodiode, the photodiode generates an imagesignal from the light radiated to the photodiode, the photodiodeincludes a photoelectric conversion layer that is in contact with a partof a P-type semiconductor layer and an N-type semiconductor layer and ismade of an amorphous semiconductor film and the photoelectric conversionlayer is thicker than the P-type semiconductor layer and the N-typesemiconductor layer.
 27. A display apparatus comprising a sensorportion, the sensor portion comprising: a plurality of pixels, each ofthe plurality of pixels comprising a photodiode, an electroluminescenceelement and a plurality of thin film transistors, wherein the pluralityof thin film transistors control light emission of theelectroluminescence element, a light emitted from theelectroluminescence element is reflected from a subject to be radiatedto the photodiode, the photodiode and the plurality of thin filmtransistors generate an image signal from the light radiated to thephotodiode, the photodiode includes a photoelectric conversion layerthat is in contact with a part of a P-type semiconductor layer and anN-type semiconductor layer and is made of an amorphous semiconductorfilm and the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.
 28. A displayapparatus comprising a sensor portion, the sensor portion comprising: aplurality of pixels, each of the plurality of pixels comprising aphotodiode, an electroluminescence element and a plurality of thin filmtransistors, wherein the pixel includes a photodiode, anelectroluminescence element, a switching TFT, an electroluminescencedriving TFT, a reset TFT, a buffer TFT and a selective TFT, theswitching TFT and the electroluminescence driving TFr control lightemission of the electroluminescence element, light emitted from theelectroluminescence element is reflected from a subject to be radiatedto the photodiode, the photodiode and the plurality of thin filmtransistors generate an image signal from the light radiated to thephotodiode, the photodiode includes a photoelectric conversion layerthat is in contact with a part of a P-type semiconductor layer and anN-type semiconductor layer and is made of an amorphous semiconductorfilm and the photoelectric conversion layer is thicker than the P-typesemiconductor layer and the N-type semiconductor layer.
 29. A displayapparatus according to claim 25, wherein the N-type semiconductor layercomprises polysilicon.
 30. An area sensor according to claim 26, whereinthe N-type semiconductor layer comprises polysilicon
 31. An area sensoraccording to claim 27, wherein the N-type semiconductor layer comprisespolysilicon
 32. An area sensor according to claim 28, wherein the N-typesemiconductor layer comprises polysilicon
 33. An area sensor accordingto claim 25, wherein the P-type semiconductor layer comprisespolysilicon.
 34. An area sensor according to claim 26, wherein theP-type semiconductor layer comprises polysilicon
 35. An area sensoraccording to claim 27, wherein the P-type semiconductor layer comprisespolysilicon
 36. An area sensor according to claim 28, wherein the P-typesemiconductor layer comprises polysilicon
 37. An area sensor accordingto claim 25, wherein the electric conversion layer comprises amorphoussilicon.
 38. An area sensor according to claim 26, wherein the electricconversion layer comprises amorphous silicon.
 39. An area sensoraccording to claim 27, wherein the electric conversion layer comprisesamorphous silicon.
 40. An area sensor according to claim 28, wherein theelectric conversion layer comprises amorphous silicon.
 41. An areasensor according to claim 25, wherein the electroluminescence elementhas a positive electrode, a negative electrode and anelectroluminescence layer provided between the positive electrode andthe negative electrode.
 42. An area sensor according to claim 26,wherein the electroluminescence element has a positive electrode, anegative electrode and an electroluminescence layer provided between thepositive electrode and the negative electrode.
 43. An area sensoraccording to claim 27, wherein the electroluminescence element has apositive electrode, a negative electrode and an electroluminescencelayer provided between the positive electrode and the negativeelectrode.
 44. An area sensor according to claim 28, wherein theelectroluminescence element has a positive electrode, a negativeelectrode and an electroluminescence layer provided between the positiveelectrode and the negative electrode.
 45. An area sensor according toclaim 25, wherein an electronic equipment using the area sensor is anequipment, which is selected from the group of: a video camera, adigital still camera, a notebook computer and a portable informationterminal.
 46. An area sensor according to claim 26, wherein anelectronic equipment using the area sensor is an equipment, which isselected from the group of: a video camera, a digital still camera, anotebook computer and a portable information terminal.
 47. An areasensor according to claim 27, wherein an electronic equipment using thearea sensor is an equipment, which is selected from the group of: avideo camera, a digital still camera, a notebook computer and a portableinformation terminal.
 48. An area sensor according to claim 28, whereinan electronic equipment using the area sensor is an equipment, which isselected from the group of: a video camera, a digital still camera, anotebook computer and a portable information terminal.